From what you’ve said, could it be that someone at this other person’s work has failed to do something, and has tried to blame you/your company to get themselves out of trouble? So maybe she’s not doing it to deliberately antagonise you, but because she has to stand by what her member of staff has told her.
Maybe?
If your boss and your colleagues are backing you up (in public, as well as in private), then you should be on safe ground.