Yes one glass is fine!!! When I was breast feeding I got nervous too, so I would have one and then pump and dump. But that was def excessive! It just made me feel better, so you could also do that if your supply is good!
Per CDC 1 standard glass of wine is safe! https://www.cdc.gov/breastfeeding-special-circumstances/hcp/vaccine-medication-drugs/alcohol.html#:~:text=Alcohol%20consumption%20above%20moderate%20levels,while%20breastfeeding%20is%20not%20recommended.
From my understanding the alcohol content of your breastmilk is the same as the concentration in your blood. Personally I just don't breastfeed if I start to notice myself starting to feel it. I don't have a wild tolerance or anything. If you think it'll give you peace of mind buy alcohol test strips!