After drops & laser mother has uncontrollable glaucoma with severe vision loss but is still functional. Will now try trab. What would her prognosis be?

Treat aggressively. If your mother already has severe vision loss, and her glaucoma is not controlled, i would advise that the pressure be addressed aggressively. She does not have the luxury of small stepwise measures anymore, as everyday her glaucoma is not controlled, she continues to lose more vision. A trab is the definitive treatment, can bring her pressures down, and is appropriate. Good luck.
Trabecuectomy. Will control pressure, requires close post operative fools up. This will not reverse the vision loss she already has. Other possibilities are the istent, this is a relatively new procedure. Ask your ophthalmologist about it.