She'll get pretty fucking blazed if she's eating brownies for her first time. The problem with first timers is that they don't know how to inhale properly, so they don't usually get high as a result of that. I smoked up one of my friends for his first time. The kid didn't know how to smoke, but in a good way. He chiefed the whole fucking bowl into a single, massive bong rip. I've never seen so much smoke come out of someone's mouth. He was coughing for twenty minutes haha. Also, he got really, really, really fucking high.

Honestly, you might want to suggest she smoke it instead. If she's never been high before, the brownie high might be a little intense.

Regarding you telling her you still smoke. I'd probably tell her when your sober. From what it sounds like, she won't care, but why risk ruining the mood when you're both high.