I think you may be already loosing if you're obsessing over this woman before really knowing her.

First, you must find out if she's interested. There are signals you'll have to pay attention to.

Secondly, you must show her that you are a stronger male than your 19 year old relative.

Thirdly, you must decide is it really worth family drama?

Fourthly, you must completely leave her in the dust wanting you instead.