My mum has been in the U S A for over 6 months expecting her immigrant visa to be sent to her as she travelled with a non immigrant visa.she got over there and my dad filed a petition on her behalf and she has done interview. both for how long will she need to wait to get the visa.

Did your Dad file for her as a spouse? if so why didn't she apply for a spouse visa from Nigeria? Is he a Citizen or green card holder? so many questions, did she leave Nigeria with B1/B2 visa? Depend on the situation, it could take sometime.

@anfanio, yes my dad filed for her and he is a citizen. he could not file for her from here becos the reason best known to him
and she left with a non immigrant visa.

It's OK. It all depends on when he filed, where they live (state) and the documents submitted. I'm thinking its going to take some months. Just be patient. However, your Dad can file for you too, now. Why wait?

If she already had her interview, the case should have been decided immediately by the USCIS officer who conducted the interview after the interview unless her background check is still pending.
She should be calling USCIS 30 days after the interview if she hasn't heard from them.

johnkent:

If she already had her interview, the case should have been decided immediately by the USCIS officer who conducted the interview after the interview unless her background check is still pending.
She should be calling USCIS 30 days after the interview if she hasn't heard from them.

Good answer. The best she can do now is wait and make some call after 30 days if no word from the USCIS.

Good luck.