I'm not talking about that dude anymore. I'm talking about you.
It's not asking permission, it's being honest, as opposed to willfully deceitful. If she wasn't ok with it, your next steps would have been on you. Either don't do it, or do it anyway (hopefully after educating her and alleviated any misconceptions).
But I'm coming from a different place on this than most. I've had some really really horrific experiences with ongoing secrets within a family, and I can almost always tell when someone is being sneaky about something. Being secretive with me is one of the worst things a partner can do to me and my emotional well being. Little secrets, no biggie. But this kind of thing is a big secret - not because of the illegality or the health, but because it is ongoing. Specifically, with me, for someone to keep this a secret, they would have to be selfish as hell (because presumably they would know how destructive secrets are for me), and lack trust in my ability to be reasonable. They would be choosing the easy route to avoid a potentially uncomfortable conversation, knowing that choice would likely cause me hurt down the line.
But, that's just my perspective, my experiences.