Hi Emily
Good to hear you are getting her seen by your vet, especially since she has messy poop and odd tummy. Do make sure they check all her teeth well. A good rabbit vet should always look at their teeth. Dental issues are such a common problem for rabbits and can lead to messy poop and gut problems.
The vet may want to test her poop also, for intestinal parasites.
How long have you had the male rabbit now? WIll you be taking him in for the vet visit also? Good idea for them to confirm he is desexed or even a male!
Hopefully Olive is not pregnant, but a false pregnancy is also possible and can cause some behaviour changes. If you have a good rabbit vet, I really recommend you look into getting Olive spayed once she is in good health. This will prevent things like false pregnancies but more importantly, it will be better for her long term health. Intact females are high risk for developing uterine cancer and/or uterine infections. The likelihood increases as they age, from 3 years onwards.