AIO for wanting to cancel my wedding after finding out my fiancée lied about a major part of her life?

I (31M) have been with my fiancée (30F) for almost 4 years. We're supposed to get married in about 3 months

A few weeks back, I found out something that totally caught me off guard. When we first started dating, we talked a lot about our past relationships. She told me she’d only had one serious relationship before me, and that it ended ages ago. I didn’t dig for details because I figured it wasn’t a big deal, and I trusted her.

Recently, I bumped into someone who knew her before we got together. During our chat, they mentioned her ex-husband. I was really confused because I had no idea she’d ever been married

When I got home, I asked my fiancée about it. She got defensive right away and eventually admitted that she had been married before. Not only that, but the marriage lasted almost four years

I asked her why she never mentioned it. She said she was embarrassed, that it was a tough time in her life, and that she wanted a "fresh start." She claimed she meant to tell me eventually, but after the first few months of dating, she felt like too much time had passed and didn’t know how to bring it up. The thing is, this isn’t just some little detail she forgot to share. We’ve been together for four years. We’ve talked about marriage, divorce rates, relationships, and our future so many times. There were tons of chances for her to tell me

Now I’m struggling with the fact that she was able to look me in the eye for years and keep something this important hidden. She says the marriage ended long before we met and that it doesn’t affect our relationship now. She thinks I’m throwing away a great relationship over something that happened in the past

My family is split on this. Some think everyone has the right to keep painful stuff from their past private. Others believe a previous marriage is something your future spouse definitely deserves to know. At this point, I’m questioning if I even know her as well as I thought I did

Am I overreacting for thinking about postponing or even canceling the wedding over this?