I'm going to tell my friend my opinion on her engagement
Did she ask you what you thought about her engagement?
I just want to share with her my thoughts about it. It doesn't mean I want to hurt her feelings.
If she wants to know you should tell her. It would be good to show you care about an important event in their life.
Don't tell me what to do. I know what to do.
Just make sure you are not offering your unsolicited opinion. This may come across as disrespectful to your friend. Ask your friend specifically if they want to know what you think of their engagement and if they approve, share your opinions with them politely.