My 11 yr old girl is not showing any signs of grief for the passing of her mother. What should I look for or do?
First of all, my condolences on the passing of her Mom (and your wife I presume?) I'm sorry for your loss....
As for your question - she is probably still in denial. Grieving someone or something is a very personal process, and I second itsbob's recommendation -you really do need to set up some counseling for her. And yourself - but especially for her, even if she says everything is fine. There will come a time when the wall she has built up around herself to keep the pain out crumbles, and the denial about her Mom's passing turns into anger and sadness - and she will need more help and guidance than you can give her to allow her to process her thoughts and eventually come to a point of acceptance. At her age, the loss of a Mother is almost catastrophic - she is at the beginning of her transition from a girl into a woman - and she is likely numb right now, and unsure about how she feels and how to process the changes and the huge void that has been left in her life.
Please get her counseling... if you can't afford it, there are groups around that will help. PM me if you need that info and I can find some numbers for you.