Poor girl, hope the surgery goes well.
There is no proof that cruciates are genetic but I believe they are. My friend has a dog that blew his cruciate, and guess what... 2 of his pups did as well. The weak muscles are IMO most definitely genetic.
Patellas are the same, although they have proven to be passed on.
Carrots are fantastic fillers grated up and mixed with their regular food. Nil calories and filling.
24/7 kibble grazing... bad Di!