I don't think it's wrong that I want to tell my friend she needs to delete her coming out post.
What would make you want to tell her to delete her facebook post?
I find the post offensive and I don't want it in my facebook timeline.
You can hide a post from your timeline, then. It's not up to you what she posts and she will probably be offended.
She announced it to the world in my facebook timeline. All of my family and friends can see it and I don't want them to see it.
If you are a real friend, you will support her for who she is rather than be ashamed.  You will feel better about your self and your friend will respect you more if you leave her post on your timeline for everyone to see.