Lay it on her and let it be. My best friends mom is the one who first suspected it in me and after she had observed the signs for a while she just asked one day when I was struggling if I had considered the possibly. She gave a general explanation of the reasoning behind her suspicion and left it at that. I scoffed at the idea initially but really I was just afraid. It took me a little time to slowly start getting more comfortable with the possibility and doing some research myself. I found this website easily through my general google research. A couple weeks or maybe months later, she brought it up again when I was struggling and since I was more educated on the topic by then and more open to the idea, we were able to talk more freely about it and start to make progress.
If you two are close then maybe it won't take quite so much time and distance to get her to reason with you about it, but I think your best bet would be to toss it out there and not press the matter too hard. She may need time to deny, then doubt, start to consider and finally start to explore on her own. It's nice you care enough to try and help figure this out.