Why does my girlfriend want to get married?Ha ha ha ur the first kind purely because of the reasons you stated. Freedom is your birth right and no one can take it away from you. It's the risk you take by taking the plunge. You obviously are not ready for a serious relationship. Don't lead her and let her down. She obviously wants to take the relationship to the next level.
we men are not animals to just look for some action and then bang bang thank you ma'am. Heck even animals nowadays (domesticated ones) don't do that.
Ask yourself whether YOU love this person (take your kid out of the picture before evaluating in the first level). This is an experience and an adventure. Invest in it the life lessons you learn are numerous.
P.S. She seems to test your commitment. Soon she is going to move on. Take a decision before it's too late.
Best of luck. Merry Christmas