Usually, doctors in Chinatown are cheap.  You might want to go there and look around.  Alternatively, if you have friends in Queens, they might know dentists there who are inexpensive. 

If your mother is here for just a short time, meaning if she is leaving within a week or two, it might make sense to use Orajel or other pain reliever to numb the pain until she is back in Nepal.  Dentist fees can break your back.  That's why I tell whoever is coming from Nepal to do all the health checks and dental work before boarding the plane at TIA.