I Killed It!

I went to a party at my friends place and she’d made drinks and cocktails and she gave me one of those long drinks and it was the worst I’ve ever tasted so when she wasn’t looking I poured it on one of her plants and now she just told me it died and she is really sad cos she loved that plant and I don’t know if I should tell her that I killed it or not. What if she knows it was me? Then I’m an idiot for not saying anything. But what if she doesn’t know? Then if I tell her I might lose a friend over a stupid drink?