This is a lot of information. So if you're feeling overwhelmed at all the rabbit care stuff coming at you right now, may save this for later.
Not all rabbits will experience GI stasis, but they are prone to it because anything that causes them pain can cause GI stasis to set in because they usually stop eating when they're hurting. There are different levels of it too. Most often it will be a minor case of a stomach upset from something they eat, that resolves itself within 12 hours and usually a few doses of baby gas drops. But sometimes it can get more serious because of a slow gut and partial obstruction, or other problem.
It's nothing to let yourself overly worry about. Being observant with a rabbits poops and eating habits, is just part of being a good rabbit owner. If she's eating, or active and exploring during her usual times and her usual way, which is usually morning and evening for rabbits(usually sleep during the day), and you're seeing normal sized poop being produced, then it's a good indication everything is usually fine.
You'll get more attuned to notice when something is off as you get more familiar with your rabbits usual behavior and eating habits. A rabbit that won't eat at feeding time, seems quiet and withdrawn, may be hunched up in a corner not wanting to move, or repeatedly changing position pressing the belly(not the same as contented flopping) and can't seem to get comfortable, and/or loud tooth grinding(not to be confused with gentle contented tooth purring/chattering), are all signs a rabbit isn't feeling well. There are contented bunny behaviors that can look similar, like flopping and relaxing, dead bunny flop, and contented tooth purring, but it's learning to recognize the other body language cues altogether, to help determine if it's a sick rabbit you have or just a happy relaxed bunny.
https://wabbitwiki.com/wiki/Understanding_your_rabbit
http://language.rabbitspeak.com/
Some emergency supplies that are good for all rabbit owners to have on hand, I would say the baby gas drops(simethicone) and 1ml oral syringes are what I have used the most. Critical care is good to have too but should only be used in specific circumstances, post neuter/spay if needed, and after illnesses when a rabbit isn't eating on it's own and the vet has ruled out bloat or a complete obstruction(can be dangerous to syringe feed a rabbit with bloat or a complete bowel obstruction). But do have CC and feeding syringes on hand before you take her in for her spay, in case you do end up needing to syringe feed post recovery.
http://www.bio.miami.edu/hare/opcare.html
Emergency supplies I like to have on hand:
Critical care - apple banana flavor, keep in freezer to extend shelf life
Baby gas drops(simethicone active ingredient)
Pedialyte(only the unflavored one, no artificial sweeteners)
Questran(rx) or activated charcoal - for emergency diarrhea only(not just mushy cecals), when there isn't a vet available until the next day
1ml oral syringes
6-12ml wide tip oral feeding syringes(normal tips get clogged)
Rabbit safe warm pack(sock filled with rice, snuggle safe)
Being vigilant is just part of being a rabbit owner. Once you get a feel for your bun and her personality, quirks, usual behaviors, I think you'll start to feel more comfortable about things. The fact that she is eating a bunch of hay is the best indicator of good health and helps prevent many of the usual rabbit health issues. If her body condition is good and she's eating lots of hay, then not too many worries there.
You can feed orchard or timothy. If she's producing healthy sized poop, has good body condition/is a healthy weight, and is eating a pile at least the size of her body per day, then it doesn't usually matter what variety of grass hay you feed. Though there are some particulars that might make you decide to choose one over the other, or a different cut of hay.
There are different cuts of hay, and the softness or coarseness of the cut can affect how fast food moves through a rabbits digestive tract. So if you have a rabbit with fecal poop that seems too small consistently but the rabbit is a healthy weight or maybe a little overweight, then a coarser hay cut may be better than a leafier cut of hay. Or if you have a rabbit that is too skinny and needs to put on more weight to be healthy then a softer cut may be better. Soft hay has more protein and nutrients for weight maintenance/gain, and coarse hay less protein and lots of indigestible fiber for weight loss and good gut motility. I prefer a medium cut that has a good mix of leaf and stem. If you want to read more about the differences in hay cuts and the particulars about them in relation to a rabbits health and digestion, I go into more detail in this thread.
https://www.rabbitsonline.net/threa...ehavior-off-after-neuter.102500/#post-1181357
A medium coarse(mix of leaf and stem) timothy hay is a good all around grass hay to feed. It's the most readily available grass hay in the US, for herbivore pets. It's what I feed my rabbits, but I buy it in bulk at a feed store as it's cheaper. It has a good amount of protein, nutrients, and fiber to help a rabbit maintain a good healthy weight, keep the gut motility functioning well, and provide for the usual amount of tooth wear needed to prevent sharp points developing on the molars, for most rabbits.
Orchard hay is one of those hays that may be preferred for better tooth wear. Particularly for rabbits with molar spur issues, as orchard is a more abrasive hay(good thing for rabbits) so may help wear down and prevent the sharp points on the molars from developing. You'll find with rabbits that it's all about the right balance to maintain a healthy weight, good gut movement, and good dental health.
https://rabbitwelfare.co.uk/rabbit-health/further-reading/body-condition-score/
https://www.pfma.org.uk/_assets/weigh-in-wednesday/pet-size-o-meter-rabbit.pdf
As mentioned, it's perfectly fine for a rabbit to eat untreated willow, or any other rabbit safe branches and leaves. My rabbits LOVE fresh apple branches. They'll sit there munching on the leaves, then strip the bark off the branch. It's all good fiber for them.
Medirabbit: safe branches and leaves
For a litter box, cat litter trays, plastic storage bins, I use a mortar mixing tray for my rabbits. Lots of different types to look at to find the right size.
Some rabbits are suspicious about trying out new foods. But usually if the food is leaf(not too long that it goes bad), they will usually eventually try it. I agree with Caitlyn, no need to wait until 6 months if her poop is normal and she's settled in well. Though I would recommend starting with non cruciferous greens. They're usually easier on the digestion and least likely to upset digestive balance.
https://rabbitsindoors.weebly.com/greens--veggies.html
Even though the breeder said you have a female, it's still a possibility for your bun to be a male. Some rabbits are very difficult to sex at a young age, and it's not until they've fully matured that you can tell for sure, usually by there being testicles that appear. That's a sure indicator
https://www.rabbitnetwork.org/educa...rabbit-care-articles/how-to-sex-your-rabbits/