Hi Copper, are you in BC?
First off, what are you feeding the bunny? Sudden diet changes can be hazardous.If he/she was outside, it's a good bet s/he was eating dried and some grass, so if you can get your hands on some timothy hay. that will be pretty close. Hay is a bunny diet staple.
Bunnies thatare used tovegetables won't have a problem with them,esp. leafy greens like carrot tops, parsely, etc, but if s/he isn't used to them, they have to be introduced slowly. Again, if the bunny was outside for any length of time, s/he should be good with greens.
You need a good quality bunny pellet, which unfortunately aren't easy to find. Pet stores often carry weird kinds with colored bits that are high in sugar and carbs and can also upset their systems (as well as make them obsese).
If you notice mushy poops, that's probably a diet thing. You can monitor a bunny's health by keeping an eye on their appetites, and espeically their poops -- if they're poops get loose or start getting smaller and/or stop, you have a sick bunny. (Start feeding him/her canned pumpkin and make sure s/he drinks. (Pedialyte is good).
How's the bunny so far?
sas
PS: Sorry I didn't see this earlier!