Hello
Squirrel20I was reading through your post and when I got to the...
"do we allow the next poor guy to fall victim to her or do we find a way to let him know what he is up against?"...I immediately gave a verbal answer.
Our daughter, too, has gone through a number of relationships. Our grandchildren were the products of two of them. Once "the glow" dimmed on her partners, she set out to win-the-war and it was indeed sad to watch...especially the custody battles. Those unfortunate guys were no match for her. Thankfully two of them have moved on...the last one not having an easy time of it. (Oh well!)
We are currently in yet another period of being estranged from our daughter and even though they went through hell, her 2 ex'es periodically keep in touch with us. Says something, huh?
I share all that because it is something similar to what has gone on with you, your daughter. Your post has made me think back to those fateful days when each of those men actually came to us to ask for her hand in marriage. Can you imagine that...in this day and age? Both those times we were in a good space with our daughter. Oh, my husband and I knew what was probably ahead for those unsuspecting men who were so in love with her. (Let me add here that...When she is good she is very, very good...but when she is bad...

!)
With that said, with each we thought...perhaps...perhaps...this might just be the guy who could be her forever-man...work his magic on reining her in...help in changing her habits. (Once again...Oh well!)
So, Squirrel20, I try hard to not give advice when I post...but in this case...strongly urge you to continue to be a silent bystander. Save yourself from more conflict. Often I have to pull the reins in on myself when I think I can be a fixer...bring those thoughts to an end by saying..."Not my problem!" Makes my life so much easier.
Huat