Dog is acting odd any ideas?

I have a 14 year old shepered mix. Sage has always been a very good eater , she would eat every thing and anything , we used to joke given the chance she would eat her self to death. You name it she'll eat it in what ever quatiet is proved and always wanted more. This past month she has been getting picky with her food. First she started to turn down can dog food which she has never done in her life before this month so we started feeding her people food such as meat, steak and chicken. She is now turning that down, but i noticed today she will eat what i'm eating (i have always gave her a little of what ever i was eating) It is very possible at her age she is getting old and sick but why will she eat what i'm eating when i'm eating and not the same meal (meat or whatever) when it's given to her? Has anyone else had this happen? I am taking her to the vet for a check up in 2 weeks.