I'm not to ashamed to say, but I've had foster sibs, and friends of sibs (15 years or so younger) take an interest in me like this. It wasn't anything romantic, it was just that they saw something different in me that they wanted to harness for themselves.
People with low self esteem often pick somebody totally opposite of themselves to try to become to sort of break out of their shell. Sometimes a hard home life, or past makes them want to re-make themselves into somebody new. An extreme case for example is my little adopted sister. I won't go into details but I was the first male that she trusted period. Her abuse was so bad that years of memory are forever gone. When my folks adopted her, she even changed her name.
It's funny now, but she's finally come out of her shell and is almost 17. Whenever I'm around she'll grab the first straw hat she can find, grab some boots and start cussing up a storm using inventive language that I was known for back when I was working on the docks. She definitely stepped outside of her self imposed prison, and remade herself into somebody else.
Some people do this more extreme than others. Think of how many people are inspired by Lance Armstrong for example, and take up road biking? Not all role models are good, but as long as she's trying to learn/emulate the good, then I don't see too much harm at this point. Try to be the best friend you can be, and look at it from her perspective.
PS, if she is trying to be the bad as well as the good, then you may want to talk to your mom, or her folks about it.