I'm going to contact a good friend through a third party and not directly
Why would you contact a third party and not your friend?
I have to talk to her about something sensitive and she might take it the wrong way.
I'm sure if they are a good friend, they'll want to hear from you directly. It's rude to insert other people into your drama.
Yeah, but she'll misunderstand if she hears it from me.
Maybe so, but it's not fair to involve someone else in this. Don't put someone else in the middle of your drama just to spare yourself some grief. You'll only complicate the situation.