There are good reasons why the Church discourages mixed faith marriages, you are experiencing some of them, and they have only just begun. Unless you can convince her that the Catholic Faith is the True Faith you will either end up betraying Christ or you will have to end the relationship.
This advice is spot on. The key for me (it is none of my business but you asked so here it is) is that you have been seeing her for
four years. It is obvious that she has no intention of converting to Catholicism and is playing you - waiting until the marriage before she tells you the truth. And the truth is this: she has no intention of being Catholic, would prefer you to become Baptist, and definitely is going to insist on raising the kids Baptist, and not ever take them to mass etc.
Run from her, now. Or your kids will never have the Holy Eucharist, knowledge of Mary, and you will find yourself held to account for your kids not getting to fully know Jesus the way you did.
Forget about you - it is all about your kids. Do you want them to never have Holy Communion? Or to mock Blessed Mary? This is where you are heading.
If she won’t convert in four years she is just biding time til marriage. She will then force you to either divorce or accept her Baptist faith. And your kids, too.
Try this on her: ask her to attend RCIA now (I know you approached it and she has given excuses for not yet doing it - and she attends Mass with you too [just to ‘play along’ for now]
Then tell her if she doesn’t convert, you two are through - see if she is willing to convert or is more willing to let you go.
(And she has probably told her parents that eventually she will convert you or at least the kids will be Baptist.)
As I said: RUN NOW OR YOUR KIDS WILL LOSE HOLY COMMUNION AND YOU WILL EVENTUALLY END UP DIVORCED.