I would stick with only the hay -- any treats with dairy (yogurt-drop-like items), nuts/seeds, etc. are technically safe for rabbits, but it's essentially like feeding a baby junk-food. They can cause upset stomach, bad eating habits, etc.... There are much better things for your rabbit that will make her happier, because it's good for her. If you find Oxbow (brand name) in the Walmart, they sell Simple Rewards treats that are much more natural and healthy. Any food that looks like a trail mix isn't recommended by a lot of rabbit owners because it teaches the rabbit to be very picky, and leads the rabbit to only eat the "junk food" bits of the food, rather than the nutritious stuff.
At this time, I would focus on spending money on good quality hay. Look for hay bags -- I prefer the Oxbow brand, but Kaytee is do-able. Timothy hay is fine, as well as orchard.
At 12 weeks, it is also generally recommended to get pellets. These pellets should be uniform -- so no trailmix with fruit bits or anything. You really want to instill healthy eating habits early. Look for timothy hay to be the #1 ingredient. Again, Oxbow has this, but if you cannot find it, look at the ingredients for other brands.
Some people may bring up getting alfalfa pellets instead because your rabbit is younger (so instead of timothy being the first ingredient, it's alfalfa). If you can only find that, that is fine too -- just don't splurge on a large bag because eventually the rabbit will transition to timothy-pellets when she's older (at the most, 6 months old, if not sooner.)
