You need first, in my view, to recognize that what's happening isn't in any way your fault. She's a teenager, and that says it all. I've been told that teenagers are testing life just as one tries on one suit after another to find the one that fits perfectly. So you need to stop worrying.
Since your husband isn't overly concerned about it, you need to recognize that your home life is stable and that affection between you and your husband is relaxed and calm. Be thankful for those good things.
If you were her mother, the situation might be different. If the girl does not recognize the healthy homelife you and your husband are providing for her, it's going to be her mother's job to straighten things out for the girl and teach her what's best for her life. Eventually, if the mother doesn't do that, the girl is going to need psychiatric help to recover from the attempts of the mother to control the girl again by doing things that may not be in the child's best interests.
The important thing for you is that you not worry and that you do not build up any guilt for a teenager's immaturity. It is definitely not your fault, it seems. Enjoy your life now; if the time comes that the girl
wants to come back to you and your husband, then you might consider offering her psychiatric help to recover from the trauma of her life--whatever that might be.
Wishing you a happy and peaceful life,