hi-
from what i understand, you feel your friend is not sober enough to take proper care of your dog.
can you hire someone else to care for your dog?
alcoholics are full of promises and in my experience, many times mean to keep them. however, the alcohol is their first love and despite their perhaps good intentions, they fail to keep their promise.
i would imagine you will have some peace of mind knowing your dog is properly cared for if you switch to another service.
as for your friend, i imagine she'll be upset but who could blame your for making sure your dog is safe? you don't do her any favors by protecting her from the consequences of her drinking.
have you spoken to her about perhaps attending AA? or giving it a try at least?