My girlfriend doesn't like DXM?

When I was younger (17-18) I used to take DXM regularly. I am 23 now and have since stopped. However, I recently met up with an old friend and we made a plan to do it once more for old times sake. Needless to say, my gf freaked out about it and told me she doesn't like it and she will be pissed off if I do it even this once end of story. I tried explaining to her that I know a lot about it and I've researched it a ton. No use. So I asked her how would she feel if I got mad at her for smoking weed everyday (which she does). Now, I have nothing against weed and her smoking it. I was just trying to prove a point. I know weed isn't the same thing as dxm (mainly because of potential overdose by careless, uninformed users) but I feel since I know the risks involved and how it affects my body that this is just a double standard, especially since I'm only doing it once. But now she won't even listen to me about it and just gets mad and tells me I'm ignorant and childish. Am I wrong here?