broaching the subject

Hi everyone. I am new to this group and hoped to get some advice. I have a 23 year old that has been clean for over a year now. She was addicted to pain killers and on the road to recovery. There has been some troublesome behavior and I'm afraid that she may be using again. She is currently on suboxone so supposedly you can't use other substances, but still there's strange behavior where she's uncommunicative and unreasonable....shades of the past that I can't ignore. We had a disagreement on the phone (she lives with her father) and she said I won't hear from her again. Her father and I have very different approaches, he enables and I have the tough love approach because I want her to do the things necessary to be a contributing member of society, like getting a job (and keeping a job). She took off for three months over a year ago and it feels like it's happening all over again. I'm sure we all know how defensive our kids can be, so other than coming right out and asking if she's using again (because you know she won't admit it), is there a different way to approach the subject? Thanks for listening.