@Awkwardmoment,
Sure, go ahead and meet.
Expect an earful of all the bad habits your bf had, how he disappointed her and her version of the fall of their marriage.
Take it with a grain of salt. She really is just trying to be "helpful." It is kinda eye-opening the difference of when he was with her and how your relationship with him could be slightly the same or vastly improved.
What helped me meeting his ex was a Herman's Head moment where the Stones "Sympathy For The Devil" popped into my mind and I laughed out loud. After that I just wasn't phased by anything she said. There were some extremely probing questions she threw at me but I declined to answer anything I felt she didn't need to know. I stuck to the basics and that was it.
Be cordial and respectful, thank her for her time. You'll only have to interact with her a few times throughout the years so chalk it up to a grin-and-bear-it experience.