My mom had a cavity that fell into her gum line and causes pain. she was now told it can't be removed because its too close to the nerve. options?

Get another dentist: Cavities should treated with either restoration or extraction. If your mom is desirous to have the tooth pulled, recommend consultation with an oral surgeon who do that kind of work frequently. Good luck with this.

Need Oral Surgeon: If cavity large enough to extend below gum line and tooth is infected, your mother should immediately see an Oral Surgeon. This can't wait. After this problem is resolved she needs to see a competent a General Dentist to make sure something like this doesn't happen again.

Root canal therapy: Ask the dentist if a root canal would save the tooth. This would be a viable option if the tooth is deemed salvageable.

Second opinion: Get to another general dentist first to figure out what is wrong in the area. It may be a dental pulpitis which may lead to a root canal or extraction possibly performed by a specialist but not necessarily. It may be caused by other issues as well but removing the filling unless it is an immune response to the filling's material isn't likely to be helpful. Get a diagnosis first.

Oral surgeon: Sounds like extraction indicated. Oral surgeons treat problems like this routinely

See an Endodontist: for evaluation. Endodontists are dentists who have at least 2-3 years of advanced training. They use advanced special equipment to diagnose and treat patients with teeth issues efficiently and comfortably.