Laser surgery to debulk or remove the tumor is a possibility if that is available near you.
Radiation might also be an option.
You might want to consult with a veterinarian who is a dentistry expert also as they do the most reconstructive work in mouths. Or you may want to consult with a veterinary oncologist as they do the most work with radiation treatments.
You can read about benign tumors here
This site has good info on how laser surgery works
You may need to find a vet school or a clinic in a larger city to get such services.
And this site mentions oral surgery is one of the great uses for lasers
Hope this helps you!
The radiation is very concentrated to the exact location where the tumor is but I understand your concerns.
As you didn't identify the type of tumor you'd have to ask your vet if this is a type that grows rapidly or slowly.
If it is invading the area of the eye socket and putting pressure there one option might be to do surgery and also remove the eye if it is giving her pain. If that has to happen what they typically do is sew the lids shut so it just looks like the dog is winking and you pretty quickly stop seeing it as a surprise. Dogs can do fine with one eye if the situation is serious enough for you to need to consider that.
Chemotherapy may slow tumor growth. A lot depends on the type it is and how far it has advanced and where it has invaded.