How can I encourage this woman to lose some weight?

I have a female friend and she's extremely overweight. We known each other for years and we met again after so many years ago. I'm not really ready for a relationship but she is wanting me to commit. I have only one problem, she's really overweight. I offered her to come workout with me. She hasn't really showed a effort into making it happen. The problem is only getting worse. I spent the night with her one night and I woke up in the middle of the night and asked her what are you doing? She said I'm eating a cup cake. I was like saying to myself "Damn, she's only going to keep getting bigger if this doesn't stop, bigger than she already is" I hate to be really shallow but I'm not into big women and getting bigger at that. Plus, she's a diabetic and shouldn't be eating like this anyway. The last thing I need is a guilt trip for leaving her after going blind or limb amputation or something. She knows the consequences of eating like that. Then expect me to be by her side and be her istant for the rest of my life. I've been there done that with someone who was disabled, it's draining and you can kiss your freedom goodbye. You have to take care of them hand and foot. Obesity is a problem in America but some people don't seem to care at all. A shame. How do you tell a woman the reason you won't commit is because she's overweight and needs to lose weight first? Maybe I should just stop seeing her and move on with some b.s. excuse but the real truth of why I won't date her so I won't hurt her feelings?