You need to pray that you are interacting with her in a Christian way, but without making your intentions known by asking her out, you are not really interacting with her in an honest way, and that is not exactly Christianly.
As Christians, we should pray about our dating life and seek God's will, right? Absolutely. However, as a Christian guy, you need to understand that the focus of your prayer on dating shifts with circumstances. This is where a lot of nice Christian guys get confused and stumble.
When you first became aware of your desire to date (and eventually marry, maybe, hopefully), you were praying to meet your potential spouse, right? You were praying that she whom God has handpicked for you will just miraculously appear. And now you met her, this girl you really like. She is attractive, nice, and "Godly" (someday I shall write an article on this confusing term), eligible in every Christian sense. Isn't this what you prayed for all along? Isn't this God answering your prayer? A ball was thrown into your court. What more do you ask for? Shouldn't you at least throw the ball back before asking for more?
But wait, you said, how do I know if this ball is "my ball"? How do I know she is the intended one? Well, my dear sir, that's when your prayer shifts to asking God to help you discern. And you can only discern through interacting with her. You need to pray that you are interacting with her in a Christian way, but without making your intentions known by asking her out, you are not really interacting with her in an honest way, and that is not exactly Christianly. So keep praying while you ask her out. Do not wait for Jericho to fall as a sign that you should ask a girl out. Jericho fell already, and in its present state, it is unlikely it will fall again. In a practical sense, if she is as wonderful as you think she is, some other guy (who probably likes her less than you do) is eying her too.
Do NOT drag your useless attempt to "know her better" beyond this before asking her out. (Read: Ask her out now: don't confuse initiation with maintenance) Do not let the window of attraction to close and shut you into friend zone. (Read: How you can be friend zoned and nuclear-rejected by a nice Christian girl who really likes (liked) you and would have happily married you)
Still need more pointers to gauge her interest? I don’t blame you. Read: The green light: signs that a Christian girl is interested.
Scared of being rejected? Read: How to break the Christian friend zone by faith and Why did God allow her to reject me?