Yes. In a word : 'nothing'' But seriously, pray short prayers for her, when you see her or think of her.
I am attracted to several wonderful, married women, but one in particular, whose prayers for me I feel, and I believe she feels mine for her ; and often I also pray for her husband, just after. Unfortunately, there is always a gender dimension in relation to my prayers for her, which can lead away from spiritual love, and when I see that about to happen, my prayer is a simple : 'Peace be with you'. That seems to put the onus onto God, and my heart doesn't get caught up carnally, though perhaps marginally, genderwise, still. Even then, sometimes, I feel I have to say to God, 'No, please Lord, don't bless her through me. You just bless her, would you please.' That way I can be sure my prayer will not be tainted, will be pure. I'm not usually as long-winded as that in asking it of Him, as I know He knows my thoughts and what I mean.
I think there are worse sins than finding kind and beautiful women appealing as women, as well as merely humanly. They don't suddenly become subjects meriting indifference or dislike, but it's part of what that great French detective, Inspector Clouseau, described as 'all part of life's rich pageant'.
It is a very seductive form of trial, because there is light and potential darkness. Though my late wife and I didn't 'turn' each other 'on' magically, as the mere sight of others could (She really liked the big, blond ubermensch type... where I'm the opposite !), but our loyalty was like our love - total. Marriage whether yours or your fancy woman's towards her spouse, should have a special, unique, divine blessing, whereby you would physically die for each other.
The more I think of your youth and the array of sexual stimuli young men face in the West, but particularly in the US, the more I sense I see in the stricter approach to your problem suggested by other posters. I have to put away thoughts of a 'fancy woman' curled up in bed beside me, sometimes ; but as a young man that could only have led in one direction.
Even then, you
will think of her sometimes, and enjoy the experience, before you 'wise up', but you must do your best, which with God's help will be good enough.
