。
My mother is unable to come visit.
Literal
Mother [topic-は] honorably-visit cannot-do.
お伺い is kenjōgo (humble form) — the speaker lowers their own side by using humble verb forms for 母's action toward the listener's side. In Japanese politeness, family members count as in-group, so you speak humbly about them when addressing outsiders. The お + 連用形 + する construction (here お伺いする) is the productive humble-form pattern; できません is its potential negative. A tight lesson in why keigo is about relational positioning, not absolute politeness.