When can I start to see improvements after an elder starts anti-depressant medication?

My Mom, age 90, began taking an anti-depressant two months ago. she's on a low dose of praxil or something like that to help ease her anxiety. she's an epileptic so we want to prevent high stress and anxiety to reduce the likelihood of a seizure. It seemed to take two weeks for the staff at her nursing home to see an improvement - less crying, less refusal to do everyday things. I see little improvement in her complaints but I'm her touch-stone and she looks to me for a lot of emotional support. I hear all the bad stuff that's going on because she's not comfortable complaining to others. I did notice that she began to joke a little more after a couple of weeks. I don't know whether to chalk it up to the anti-depressants or getting used to new surroundings. Hope this helps...