S.S.
I couldn't agree more with Janine A's response. I think she nailed it pretty well! If you think you can confront your friend with your concerns for her and for the situation, that may go a long way.
Depression can compound itself if people are oblique and fearful of hurting someone's feelings. My family walked on eggshells for years around one of my sisters who attempted suicide in college. Ironically, the fear of making things worse is often perceived by that person which just makes them feel worse, believing that they really are losing it and really are disconnected. It also can give them a twisted sense of power that they may or may not really want.
As I've dealt with depression in myself over later years, I find I appreciate those who talk directly with me about their concerns. The eggshell dance is not fun for either side involved. Confronting things honestly and with love may not be the easiest route but often is the most productive for all involved in the long run.
If your friend is getting professional help that is productive, that is great. But just because she's getting "professional help" doesn't always mean it's helping. You might ask if she feels like she is getting the help she needs. If she has a spouse/family, is her spouse/family supportive? Is she accepting of her depression and willing to address it, or is she denying it? Is it being dealt with via meds, talk therapy, or both? You might feel like you're prying but it may be the candor that is needed at this point, if it hasn't happened already.
My husband keeps wondering when I'm going to get "cured". However, getting "cured" isn't the goal as much as "managing my symptoms". It's a subtle but significant difference. (Someone with diabetes may not be cured but they can manage their symptoms with care. The same goes for depression.) For all I know, I may always have to manage my symptoms. When I'm managing them well, with meds and talk therapy, it might appear to someone that I'm cured. But the truth is, the potential is always there. To some people, that may sound hopeless. But it's just a reality of managing one's life with a disease or dis-ease. That's why maintaining good self-care is critical.
Best of luck in dealing with your friend. You need to take care of yourself and know what bounds push you and your relationship (business, friendship, family) too far. Maintaining healthy boundaries of what you'll accept and not accept may help define things in a much more positive way. And, in the long run, may do more to help your friend than you think.
Good luck!