It may seem cruel but pulling away from these types of people is often the best move you can make for them. A heroin addict doesn't need to be handed more heroin, they need to hit rock bottom and suffer through the withdrawal so they can reorient themselves.
Joseph's story from the Bible is possibly my favorite story of all time, and it actually nails this issue perfectly. You have the favorite son among 12 sons, second youngest of the bunch, seemingly spoiled, daddy's little snitch, etc. who gets unfairly (though maybe understandably) eviscerated by his jealous and spiteful brothers when they sell him into slavery. Despite this betrayal he continues on with his head held high and succeeds in a position that seems rather depressing and hopeless.
Later on when he encounters his brothers again he doesn't just take them in with wide-open arms. He tests them, and he tests them rather harshly. He orchestrates a scenario to see if they learned their lesson by observing their behavior. Only after they pass his test does he make himself known to them and rejoice in their company once more.
The wisest paths would seem to be:
- Refusing to enable or even entertain poor behavior in others.
- Following some kind of a "fool me once shame on you, fool me twice shame on me" mantra.
- Rejecting those who bring you down. Their behavior severs the unspoken social contract of trust, and you should only let them back in your life after that trust is properly restored and rigorously tested.
- Attentively judging people based on behavior and action, not words.
- The most difficult of all, staying as strong and positive as possible in times of harsh suffering and betrayal. Should Jenifer in your scenario choose to be spiteful toward Rachel and do something to "get back" at her, it just makes everything in Jenifer's life that much worse.
Rachel is essentially an embodiment of a black hole. You can throw as much as you want into it -- you'll likely never see it returned. I recommend cutting people like that off entirely. If they work themselves out down the road then maybe, maybe you give them another chance after they prove themselves.