I really wouldn't message her, she's irrelevant.
She's actually pretty pathetic; cheating with a guy who messes women around a d has who knows how many on the go .. don't know what her fiancé is like but it seems unlikely he's worse than your dh's friend. He could give her STDs (and she could give them to her fiance if she goes back to him). She obviously doesn't esteem him enough not to.cheat on him, and withba scummy man whore at that, so she's engaged to someone she doesn't value... Sounds like it's all about getting a sparkler in the finger and settling at the right time, her engagement is a farce a d if she married him, her marriage will be too.
Then there's the buying people .. like wtf.
Not only is your dh's mate using her for sex etc alongside other women but he's using her for money a d lifestyle too. He's even got her treating his mates. She's sounds like she thinks it's the only thing she can do to impress and bond with them. That's actually pathetic, she must actually have really low self esteem.
Always playing mummy Warbucks - can't just get to know people and form a normal,natural bond/friendship with them without trying to buy them.
So she she hasn't got an authentic relationship/engagement, she hasnt got authentic friends and her relationship is based on shagging a man whore and financing him.
Meanwhile she's trying to act like you don't exist so she can have another "devoted", admiring bee to her queen - except they're not devoted or admiring; they're using her and bought.
I know her behaviour is very annoying but she's pathetic, her salary is not matched by any self respect of sense. Forget about her.
DH is the real issue apparently.