My Mother Has Developed Overlapping Front Teeth and Has Pain?

Your mothermost likely has developed periodontal disease.  Periodontal disease causes bone loss which in turn can cause teeth to "shift" and "overlap"  The pain can be associate with the bone loss and inflamed gum tissue.  Basically it is a chronic infection of the gums and surrounding bone around the roots of her teeth.  This can be detrimental to her overall health.  Have her see a dentist in your area he/she will be able to diagnose this and treat her appropriately 

Teeth very rarely start overlapping significantly when someone is older unless they have advanced periodontal (gum) disease and the teeth would be very loose.  A dentist should be able to diagnose that.  Not sure what the problem is but it could be in her head

I am quite familiar with this situation.  Due to lack of consistent oral hygiene care, your mother has developed periodontitis (gum disease).  The inflamed gums have caused some bone loss around the"overlapping teeth" and they have shifted due to pressure from the lower teeth.  Being that your mom can no longer practice good oral hygiene (brushing, flossing, rinsing) I would advise professional cleanings every 2-3 months, with sedation if necessary.  A caregiver should attempt to brush her teeth at least once every couple of days as well.  Good luck.