Paleo, Veganism and Depression

Hi all! Hoping everyone is well and safe this Sunday. I know we in the South are enjoying our first true day of Fall and those of you in the NE are in my prayers as Sandy comes through.
I need some help. I have a 13 year old 'niece' (cousins' daughter) who is very depressed. She is a twin and her sister is one of the happiest, live on the surface girls I know. But R is not. She has always been moodier than her sister and as she hits those teenage years it is getting worse. I found out yesterday she has been seeing a counselor but refuses to really talk. Her mother and step-mother who she lives with are vegetarians and she is vegan. I am convinced that this has a lot to do with what is wrong however; I have no idea how to even begin to approach this. They are surprisingly not all that open to change of any sort and of course convinced that meat is bad. R will not even eat anything w/ gelatin in it. She does trust me and will talk to me more than most so I am hoping for some ideas on how to start talking to her about changing her eating to help with the depression.
Any and all ideas are very welcome!
You know all those things you have always wanted to do? You should go do them.
Nah.. I was always aware "they" were out to get me.. even before I became Primal..... Now I can just run faster if they find me-Dino Hunter
Age 46
height 5'3
SW 215 lbs
CW 180 lbs (whole foods/primal eating)
LW 172 lbs
GW 125ish lbs