Is she just more Mature in General or just Spiritually more Mature?
Cause... If its just that she seems to have an enviable relationship with God, then I don't think its a big issue. Having someone who takes their faith seriously is important.
Then again, if you find that you do not add to her ministry, she may not want you involved in her life.
When Two Mature Christians size each other up to find out if its going to work they have to consider that their Passion for God might pull them in different directions. If you are willing to Support and protect her, Financially, Spiritually, Physically and Emotionally, then its almost better that your not as Mature as she is.
Think of it this way. If you are a Sports fan and you want to find a woman who is a sports fan too. Both of you being really Passionate about it can lead to it being a Rivalry within your home. Which since its sports isn't that big of a deal that she has her Jerseys and team and I have mine. When it comes to Faith, if she takes it really seriously and you do to, you might find yourself having Passionate heated arguments about things that most Christians never think about.
If she is as Mature a Christian as you say she is, she may not retreat from a position that you disagree with her on.
I would say go for it. Be a Gentleman, be honest and don't feel intimidated by what you see in her.