I think I forgot to express my condolences previously. So...
My condolences for the loss of your mother.
I notified Social Security, credit cards, etc myself and advise you to do the same. Social Security was easy (one phone call which was answered by a very nice lady). My dad died on the fifth of the month, so we were able to keep his last payment (he was still alive when it was sent). Regardless who calls, they will eventually find out once other public records catch up (it takes a few months).