Don't introduce any new foods, especially sugary foods or grains. The exception to giving a new food, is a good quality grass hay, which is usually the best food to feed a rabbit to help prevent potential digestive issues.
Feed the same exact foods she was getting in her previous home(unless that food is making her sick and/or causing digestive issues) for the first few weeks, as she gets settled in. Make sure she's eating her food normally. Once she's settled in for several weeks, then her food can be gradually transitioned to a different one if you want to change feeds, or if her current feed is an unhealthy one. If she wasn't weaned properly or if she's overly stressed being in a new home, she may not be eating her food well. In which case, other measures may be needed to keep her eating, and try and prevent digestive illness occurring.
https://rabbitsindoors.weebly.com/pellet-food.html
If she wasn't fed a good quality grass hay(horse quality, no mold), I would suggest providing some that has plenty of leafy strands(not too much of the hard stems). A good quality soft to medium soft grass hay, is going to be the best thing for a baby rabbits sensitive digestive system, if she will eat the hay. Make sure she always has hay to eat(never should run out).
https://wabbitwiki.com/wiki/Hay
https://rabbitsindoors.weebly.com/hay.html
Try to keep her in a quite place if she's very nervous around people, and especially don't be picking her up and handling her if she's not perfectly comfortable and happy around people. Minimize anything that is stressful to her, as stress of a new home and weaning, can cause baby rabbits to develop very serious digestive illness.
Normally it's recommended not to be picking up rabbits except when necessary, as most dislike it and it can cause them stress(also risks of injury). But with this being a very small baby, if she's used to people and very comfortable around people, it may be comforting to her to snuggle in a lap and to be near you. In this case, it would cause her less stress to be cuddled and to be around people. Though I would advise great care in handling her and doing it over soft surfaces close to the floor or other safe surface, as baby rabbits can get squirmy and could get injured if a fall occurs.
https://rabbitsindoors.weebly.com/bringing-your-rabbit-home.html
If she's nervous and/or there are some issues with her current diet, and she starts to develop mushy poop, but there are still normal fecal balls being produced, then some changes may need to be made. If she stops eating and/or develops watery or mushy poop where there are little to no normal fecal balls being produced, this is true diarrhea and considered an emergency and you will need to have your rabbit seen by a knowledgeable rabbit vet immediately. In which case,
@HalaBuns may have a vet recommendation for you.
https://bunssb.org/bunnies/guide-bunny-poops/
Medirabbit: bacterial enteritis/diarrhea