Does she have a good sense of humour? Because I had a similar situation once and invented the “Monty Python” offensive. Specifically, we made up a silly song (along the lines of the “SPAM” song) and all broke into it the next time he complained. From that time forward, without fail, if he started whinging, we started to sing. Eventually he would just hum the tune quietly to himself, we would chuckle, life got on and all necessary communication had been achieved quickly and without negativity.
But only if she has a good sense of humour. . . if it’s a PMS thing that approach could end badly.
Do you get together outside of D&D? Maybe, despite her bitching, she really likes everyone in the group and doesn’t want to feel left out. Or she’s so insecure she thinks you’ll all be talking about her if she isn’t there. Maybe suggest she stay at home and then everyone have dinner together after, or something similar.
There may be something you don’t know about, like past infidelity, but low self-esteem is likely enough to make her jealous.