If this seems to be an isolated incident, a momentary case of who-knows-what, then I’m inclined to agree with your husband to let it go – while taking a few minor steps to discourage her sticky fingers in the future. But if this is part of a larger pattern of bullying or a sign of possible dementia, then it needs to be taken more seriously.
Capitalize on your previous collaboration. Did he approve of your preschoolers licking subway station handrails? Probably not. The same risk-assessment mindset should apply to parenting teenagers. It’s just a bit more complicated because you’re trying to instill in them the desire to make good choices themselves. Above all, make sure he knows this isn’t about his life path – and help him separate the concept of reasonable protection of your children’s safety from judgment about him as a human being.