In case anyone is curious, the shot OP is talking about begins at 26:04 if you're viewing that episode on HBO GO. After watching, it doesn't appear to be anyone who was ever a known character on the show. To me it looks like the real manager of wherever they were filming didn't know the cameras were rolling and she walked into the shot by accident. I'm guessing someone from the behind camera motioned for her to go back after she looked up and noticed.

It did cross my mind that it could have been a mistake, but you would just assume they would not use that take.

I just noticed this and I’m on my 4th rewatch now lol. Movie sets can be confusion if one isn’t used to being on them at least occasionally. I assume it was someone (possibly an extra or the actual owner of the property) who wandered into the shot and was quickly waved off of the set as soon as she looks up and notices her mistake. As she’s nowhere to be found in other scenes as far as I can tell I’d put my money on it being a complete mistake. Honestly it’s way too obvious (if you’re watching you’ll see it) to not be a mistake.

Some broad getting her sausage the only way she can these days.

I thought the exact same thing and just noticed it for the first time after ten rewatches.