Just my opinion, take it for what it's worth.
I would give her a chance. Just make sure that she stays in your or your husbands sight and keep her away from the computer.
Sometimes being at a family event makes the addict feel like they are loved and is very helpful to their recovery. It sounds as if your husband's family is the perfect place for her to be for her first time back home.
If she wants to stay clean, she will focus on the family event, if she doesn't, she can find a cell phone and a computer anywhere (and you already said that)
I hope whatever you choose, that YOU have a fun time and a good day.