Rebecca McGill was Charles McGill's wife and a famous violinist. It is assumed that Rebecca left Chuck after his phobia began.
In a flashback set in 1992, Rebecca and a hypersensitivity-free Chuck, prepare dinner. Chuck apologizes in advance for the guest they’re expecting: Jimmy, whom he describes as “an acquired taste.” Rebecca isn't worried, but they come up with a plan in which she will tug on her earlobe if she tires of Jimmy's antics and wants to end dinner early. The couple is interrupted by the doorbell. Six-pack of beer in hand, Jimmy looks at the house in awe. Chuck impatiently invites him inside.
Over dinner, Chuck boasts about Rebecca's impressive career as a concert violinist. When Jimmy awkwardly brings up their wedding, Rebecca kindly changes the subject and asks Jimmy about his first week in the mailroom at HHM. The conversation lulls to an uncomfortable silence, so Jimmy begins telling lawyer jokes. Rebecca smiles, genuinely amused. As Chuck heads to the kitchen to retrieve dessert, she jumps in with a joke of her own. Rebecca and Jimmy dissolve into hysterics, both too preoccupied to notice Chuck pulling at his earlobe, his fake smile beginning to falter.
While reading in bed later that evening, Rebecca tells Chuck that he shouldn't have worried so much. As she turns back to her magazine, Chuck takes a crack at a lawyer joke of his own. It falls flat. Rebecca humors him with a polite chuckle, then resumes reading. Chuck stares straight ahead, jealous of Jimmy’s natural charm and the effect he had on Rebecca -- one that Chuck couldn’t replicate. ("Rebecca")
It is later revealed by Jimmy that Rebecca left Chuck, though it is unknown why. ("Witness")