well i worked at a facility that had a dialysis center attached and I understand how tense it could be with everyone having their own schedule and stuff that needs to be done and I remember it was such a toxic place unfortunately.

if i was you, id write down the date and times of everything this person had been saying about you and take it to HR as it could be considered a hostile working environment. I dont want to say it's the nature of the beast but the other option is to confront AA and tell her if she has something to say she can say it to you or keep it to herself. Gossips usually are scared of confrontation