HI Laura, I really feel for you, Its like reading a book on myself when I read your post, My mom was diagnosed last October and I cried for weeks and weeks, uncontrollably sometimes. I live alone with my mother as my father passed a long time ago now. I didnt take anti depressants as I have found in the past that a good girlie night out works, I have the best group of friends in the world who i can ring or call to anytime, we just go for a drink or the cinema or anywhere really and it does help. Some nights i just sit and cry and they just hold me, it really works!
My sisters seemed to be coping so much better than me and i thought I was losing my mind, but I since discovered they were in denial and as mom got worse so did they, whereas I was holding it together. I think in the beginning I was almost grieving for my mam while she was here! In a way I was, as she is almost certainly a different person, we dont do any of the things we used to , she can barely leave the house, but we still talk and laugh a lot. And open a bottle of wine most weekends! This does help, trust me Im Irish!
Anyway hang in there, and just be there to do some of the normal things not just doctors, shopping laughing dancing if possible, they really appreciate to not feel so disabled, and they also like to think that they are not ruining their childrens lives, (something she used to say) So make sure you talk to her and have fun with her, you will be happy those times!
Take care