Find out what she was being fed, do NOT just give her any old pellet, if there is a change in diet it should be made gradually, as in mixing in some of the new pellets with the old brand etc etc until the total change is made over.
bunnies have an ecosystem of bacteria in their guts that digest their food. The various kind of bacteria live in a balance to the sort of food the rabbit is eating, if a big change is made, they don’t have the particular balance of bacteria in their gut to handle it yet and it can lead to trouble, but if the change is made gradually the bacterial flora change balance along with it and all is well.
baby bunnies eat their mom’s poops to get the right bacteria in their gut for the foods they will be eating.
It’s not a good idea to change the diet drastically, all pellets are not equal and vary tremendously in make up. Please find out what brand your bunny has been eating and get THAT one. then, when the other pellets come, make the change over gradually