My son is behind on speech/language and goes to preschool for it. They try to have him look at their face when talking and encourage him to talk to ask for things (he often points and grabs fingers to 'lead' people). For you sanity, you may want to encourage her more physically - grab her shoulders and steer, grab her hand and point at things with it so she learns to do it, and work on learning small commands like "put this in the garbage", perhaps demonstrating it a few times first.
One thing we have done at home that really helps is the Letter Factory dvd by Leap Frog. It's a cute show where they actually teach the letters to talk (ie, a monster scares all the A's so they say AAA!) At first my son wasn't interested in making the sounds, but he liked watching it and now he is practicing his letters as well as pointing at letters on my shirt and saying the corresponding sound. There is a Talking Words Factory DVD that is on it's way also, where the letters are combined together to make words.
I think preschool has helped, and being around lots of other children is a big encouragement since he is our first child. There's something about seeing your peers talking tha makes you want to too, right?
The shock of having her mom gone could be a factor, in fact I know of a man who watched his mother die at a very young age and immediately developed a rather severe speech impediment.
Best of luck.