Would it be dramatic to tell the GM?

I work in fast food and am a new manager. I just came back from being sick and got scheduled with someone I consider a strained friend/comanager because she gets snippy at me a lot (people on here have told me that she seems to be on drugs) and 2 other people. For a lot of the night she left me alone, on the phone. I didn’t care until now. When. She went to the gas station next door to get medicine for one of them and when she was leaving, our grill person wanted to go outside and smoke with her. So she invited them to go outside too. As soon as they left, we got slammed. So I was stuck doing both the grill work and up front work by myself, so after 4 orders, neither of them were back. I told the other person they could stop taking orders for a few cars so we could catch up. Especially since they haven’t really trained me on grill much. As a result of this, a lady cussed me out and threatened to try to get me in trouble. I know it’s def empty threats, especially because she claimed to know the manager “personally” when it was clear she didn’t, but it’s still frustrating. I just came back and friend could tell I was still under the weather. So I don’t get why she would put me in a situation where I’m left alone. And then to make it worse, after she came back I told her, and all she said did was make a joke about how I “can be sometimes” and how I’ve “been called worse”. 😐

Part of me feels like it’s not a big deal. But another part feels like she screwed me over and doesn’t even care.