Well, I don't think it is her business. If she prefaced it by asking you if you were interested in a volunteer opportunity, it would have probably been more appropriate though a bit presumptuous as you are private about your health. I wouldn't know what to make of someone just handing me a pamphlet like that. In truth, I would go somewhere else to get my haircut. But, that is me. I find it easier than going back to ask 'why' (I'm not good at that sort of thing) and I would have been hurt. However, you have known her over a period of time and if you are comfortable it is probably a good idea to ask her what her intentions were by giving you the pamphlet. She might have good intentions and didn't know how to talk to you. If she is not nice about it, then you can decide if you want her to cut your hair anymore or not. It is up to you and your comfort level. I would have had the same initial reaction as you: shocked and embarrassed. I did get an anonymous letter with information about depression one time - and I was already being treated for depression. It did nothing for my social comfort, wondering just how much I stood out to others and how. Not really good for depression.
Best to you, LM