It is common for a rabbit that is barely weaned to have a very fragile unstable GI tract ; diarrhea in an infant is really serious; she is going to need fluids with electrolytes to keep her from becoming dehydrated from diarrhea.
If she is actively drinking get some pedialyte and put it in another water bottle or bowl to see if she will drink that instead of plain water.
There is also a product named benebac that is sold at petstores like Petco ; it is a probiotic that contains live microorganisms that help the GI tract produce beneficial bacteria and can stabilize the ph in the gut ; it is sold in mini tubes for small mammals and also in a powder form for cats and dogs ; the dog and cat benebac can be used on a rabbit. If you can get it give her a dose.
There is also a product called the Biosponge which is an oral formula usually used in horses ( but effective in treating many mammals) which helps bind the toxins being produced in the GI tract ( usually clostridium) and eliminate it from the body.
People who own horses may have some of this formula and could give you a small amount to use.
Metronidazole also can help an inflamed GI tract but that would come fromthe vet
Ican give you a link to explain this condition, however,I realize that the materials needed to treat it are not readily availabe to a layperson and would need to be prescribed by a rabbit saavy vet
http://www.bio.miami.edu/hare/poop.html
In the meantime continue to attempt to give her hay rather than anyother foods and keep fluids going in
