DalM0m, you're doing the right thing - and frankly, you have nothing to feel guilty over.
I'm just going to throw one thought out there: You say that she's a dear friend, so I imagine you're the type of person who accepts others warts n' all. Thing is; I think that the ability to be honest with our friends is important (of course done in a tactful manner) and this is clearly a sticking point right now. Is the problem that she would hate you if you were honest about the outcomes of trying to help her in the past? If so, I just wonder about having a friendship with someone who can't see fault in her own actions...
For what it's worth, I too would probably also just say "I can't help", but the lack of ability to be honest would really bother me.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.