I've had people self-destruct while playing me in a traditional 4-stock, 8-minute time limit match. They self-destructed VOLUNTARILY, and as soon as I saw that they did that, I immediately ended the match and said something like "Dude, don't do that - it's not a fair match anymore." Basically, I didn't want my opponent to be crippling himself because that would give ME an unfair advantage and therefore make the game invalid. It depends on how you look at it...I looked at it as a breach in the "fairness" of the game, and, being a pretty competitive person, I like things to be as fair as possible. If my opponent voluntarily makes it easier for me to win, I don't like that - I want to be challenged and I don't want my opponent to "help" me to win.. That's not to say that you still can't end up winning if you self-destruct (you did, right?), but in my case, I'd feel bad because I'd technically have an unfair advantage. That's why I ended the game - the girl you're playing with seems to have a different reason for disliking it, and, because I myself dislike it when people do that, I'd say you have to respect that.
Of course, in tournament play, if someone self-destructs, you can't re-set the game or get mad - rather, you'd only count yourself lucky and take advantage of the fact that your opponent is now one stock down from you without you having done anything. However, when playing non-tournament matches, I would still end the match if my opponent self-destructed because again, it's giving ME an unfair advantage (in my opinion) and I'd rather not play with such an advantage. In tournaments, anything that happens WITHIN THE GAME is considered "fair" (excepting banned things like stalls and crashes), and thus you have to treat it as such, even if it's really not all that fair.