Thanks for the advice. I have noticed a bit of an improvement already, so I think she is starting to gain. She also isn't dehydrated, I checked her skin and I see her frequent the water bowl several times a day.

I'm pretty sure she was stressed because we were gone and also because she and Pippin don't always get along and sometimes when I am not there he bullies her by staring her down. She was probably upset. I've started to let them outside separately (they have an enclosed cat area outside) for an hour or two each day and I think that calms them down so they don't have staring contests.