I am a U.S. citizen. I filed an immigration petition for mother last June. It is serviced by the California Service Center. I am not sure how long this process takes until she gets the visa but since she is in a desperate situation have lost her husband a month ago, I would like to bring her to the U.S. asap. Is there anything she or I can do to speed her coming to the U.S.? For example, would applying for a visitor visa be advisable?

If she just wants to visit, why not?

because she has NO intention of "visiting",...this clown has already filed for her to STAY in the US (thus negating the term 'temporary)...wait your turn...your mom is NOT a tourist....period.

She can come on B-2 visa to visit, but it would be very difficult to convince consular officer that she intends to return home, given pending application for immigrant visa.