How do you know you like her?
This is a big part of approach anxiety...
Take this approach:
You like HOW SHE LOOKS, but, you don't know if you like HER.
Make it your mission to get to know her on a personal, emotional, and intellectual level. If she meets your criteria for a STR/LTR, make the move.
You're already validating her by saying you "this girl I like". Make her work for your approval, keep control of the situation, and stay on top.
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If you take that approach, you can always validate your approach by telling yourself: "I might not like her, lets find out if she meets my standards." That way, there will be no fear of "Does she like ME? Will she accept ME?" You flip the script and put the pressure on her instead.