Is it safe for my 84-year old mother to have surgery for glaucoma. Has glaucoma but otherwise in good health.

Yes. There are almost no medical problems that would prevent this type of surgery.
Yes. If surgery is indicated to help treat her glaucoma and preserve her vision it is safe because of her age and health (age is not a contraindication). As with any surgery, there is associated risks. You should discuss this and her options with her eye md or glaucoma specialist.