I'm going to tell my friend her relationship began as predatory. Think that's the right thing to do?
What does a predatory relationship even mean?
It means
I don't really see the connection here. There is no harm being done here so you shouldn't advertise this relationship as harmful if there's not basis for it as it may ruin what is otherwise a good relationship.
I'm really pissed that my friend believes the guy she's dating is innocent. This has caused me to lose sleep so I have to tell her what happened and see how she feels about it.
You are best just leaving them be and not getting involved. I don't think you are going to fix anything for them and she will probably stop being your friend if you won't let it go.