Like Magic says, I think this woman is getting a hard time. All these LTBs because she has dared to say that she's jealous.
Being with someone who has DCs from a former relationship comes with a whole host of issues, as the step-parenting board shows. Post again on there and you will get a more balanced view.
Of course someone who is openly hostile to your DCs is a no-go, but you say "She has met them a few times and was great." Sounds to me like someone who is trying to do her best in a tricky situation and trying to be honest with you.
If you want to continue in a relationship with her then use her honesty to open up discussions about how things will work in future.
My DP came right out with the whole "my DCs will always come first" business the first time we met. It should go without saying that your DCs are the most important people in your life. That doesn't mean it isn't hard when I can't see him for days because he's spending time with his DCs. I wouldn't necessarily use the word 'jealous' but there is an element of compromise involved in these situations and if someone is feeling resentful but unable to voice this, it's not going to end well.
We both have days when we wish we'd met sooner, that's not trying to erase our pasts, but accepting that life would be simpler if we'd been the ones to get married and have DCs together, rather than having to deal with interfering exes and the guilt of feeling torn between our separate responsibilities.