What Causes Continuous Pain To The Underside Of A Tongue?

Pain under the tongue could actually be any number of things. It could be something as simple as a mouth sore caused by being poked or scrapped by a piece of food. It could be caused by a mouth infection or it could something very serious such as a cyst or tumor (or even mouth cancer). It could be an abscessed tooth that could be affecting (or infecting) the gums and tongue. Try swishing some warm salt water 3-5 times per day. If it does not go away or feel better within a day or two, she should return to the dentist for more evaluation and treatment. (Have the dentist take x-rays or do a blood test--something more than just a glance).

You should look up a homeopath or herbalist in your area.  A lot of things have causes which the regular MD or Dentist has no idea about or refuses to learn about.  Ask around your community or visit a local health food store to acquire some contacts.  You might be more than pleasantly surprised.  More and more people are turning to "alternative medicine" with remarkable results of better health.