If you're comfortable in your relationship - then it doesn't matter what she does; your partner isn't interested and what she does makes not a jot of difference to you.
The high ground is to just do nothing; but if I was you, I would take solace in the fact she is hitting on the person you're engaged to - and would make a point of being disingenuously nice to her, so as to rub her nose in it.
She'll eventually get the hint.
bawjaws2000 t1_jegkc56 wrote
Reply to Neighbor’s worker flirting with my fiancé I’m 24F and he’s 27M by IndependentLoud1671
If you're comfortable in your relationship - then it doesn't matter what she does; your partner isn't interested and what she does makes not a jot of difference to you.
The high ground is to just do nothing; but if I was you, I would take solace in the fact she is hitting on the person you're engaged to - and would make a point of being disingenuously nice to her, so as to rub her nose in it. She'll eventually get the hint.