You can do this by being agreeable, friendly and continuing the conversation in a non-threatening manner.
This goes the same for both genders.
Otherwise, why would she bother doing research? They naturally touch your arm so as to make a point, or hug you to the point of crushing you when saying goodbye.
She might also stand a little taller and push her shoulders back to expose more of her neck.
Specially when you may be around.
Is she winking it just a tic at you or is?.
You'll find her constantly complaining about being single or about the relationship she's currently in and out of like clockwork She'll find a way to work it into ever conversation.
This is expected when you're actually in a sexual relationship with her, but when it comes to just being friends, you'll find it happens all too often and if you pay close attention.