Ways to find out? ways tell her?

Well dear, she probably does like you. You guys have a lot in common with her and she's always teasing you right? Thats the way us girls are all the time. The best thing you can do to tell her you like her is just come clean and get to know her better. She probably is scared to tell you, since that's the way us girls think sometimes and hold back what we feel. If you make her feel comfortable and make her feel relaxed to be around you, she will defiantly open up to you what she is feeling towards you and you will know the truth. I wish you the best of luck with you and your friend.