OK. I’ll grant that as a possible interpretation. However ... “Spiked” usually refers to adding alcohol to what is normally a non-alcoholic beverage.
I think this statement makes it pretty clear that there was more than alcohol in the minor’s alcohol. So, it was a "spiked" drink. I suppose alcohol was used to get the girl to drink anything, in the first place, and possibly cover for the effects.
I agree that the description is oddly written, and I had to read it twice to understand what was being said. If it had said, “an alcohol spiked drink", I would think your interpretation was correct.