Oh my!! - it's always something - isn't it??? Hopefully that mass is something that won't effect her adversely. Try not to worry - I know - easier said than done!
Is she taking anything for the pain of the spondylosis? Unfortunately I know first hand how uncomfortable that is.
Lots of prayers and well wishes from me and the poochies.

BTW - interesting fact about the FF. My son's 2 cats split a can at night - maybe that's why their bellies are swaying when they walk. They get dry food the rest of the day to nibble on when they're hungry, but don't really eat much and I could never figure why they are so chunky.