If there is enough bone to place implants for an upper denture only, she could wear an implant denture which would not cover the roof of her mouth (so she shouldn't have a gag reflex with this). However she needs something on the bottom arch for the upper teeth to bite against. If the upper teeth have nothing to bite against the bone can begin to resorb and then the implants might fail.
Perhaps her dentist could place a partial lower implant instead of a full denture implant or she could have a bone graft to improve the success of other implants.
Full arch dental implants by: David
Full arch upper and lower dental implants with fixed bridges not dentures $25000.