Search Results: girls being too pushy

There's this girl I like, and am friends with (I haven't explicitly told her I like her), who has suddenly started avoiding and generally not being her usual self towards me. Let's call her L. This started happening after her birthday a month or so ago. Before that point, the two of us were hitting it off quite well, and I got the feeling that she may have liked me. L's a generally quiet girl, rarely initiates conversation, but will flair up when talked to.

The potential problem, however, is a mutual 'friend', let's call her M. M is a recent ex girlfriend of another friend of mine, let's call him R - M and R's relationship ended badly. I wouldn't put it past M to use the fact that I am friends with R to get into L's ear to get her completely offside with me, especially if L told M that she likes me. Call me paranoid (which means I could be completely wrong), but considering L's attitude towards me suddenly changed after her birthday, when she would've been talking to friends, including likely M, I can not put it down to anything else, but at the same time I obviously don't and can't know for sure.

I asked L what's up and told her I was happy to talk things over. She put it down to study and work related stress, and said she was fine and not to worry. I never intentionally did anything to offend her, and I made a point of saying this when I talked to her about it, but she's still being 'off' towards me, despite this.

How can I get through to L without seeming too pushy? Particularly looking for girls' opinions here. I have another mutual female friend who is trustworthy, should I talk to her about it and ask her to talk to L on my behalf? I don't want to lose any chance I may have with L, especially only for being guilty by association.