It’s really difficult to come back with a clever answer in the moment so don’t be too hard on yourself, it sounds like she’s a pro at the barbed comments and can hit the spot. It’s natural to freeze when someone does this, also I would imagine you’ll be on your guard with her waiting for the next remark.

I did once read a good response to such comments “Did you mean that to be as hurtful as it sounded?” it puts the ball back in their court, addresses the issue but doesn’t go down to their level. Whether you feel that’d be appropriate or not I don’t know.