Am I overreacting to a coworker acting like she still runs the place after months away

So at my job, we don’t have official leadership titles, but there’s definitely an unspoken hierarchy (in my boss’s mind at least). Before one of my coworkers (we’ll call her Jess) left for a few months, she was the go-to backup for our team lead. I was basically next in line under her.

While she was away, I stepped up a lot — I was consistently taking the lead, trusted with key responsibilities, pulled into planning meetings, getting the same bonus pool as the lead (which is based on seniority). Basically, I’ve been putting in the work, and it’s been recognized.

Now Jess is back… and it’s been awkward.

On one of her shifts, she told me to complete one of her basic open-up tasks — which she hadn’t done because she’d gotten absorbed in this non-urgent organizing job that easily could’ve been done later. I didn’t say much at the time, just did it and moved on. But since then, it’s kept happening.

On another day, I politely mentioned that we now do one of our standard procedures differently (it was something our boss asked us to change months ago). I said something like, “I know it feels wrong at first, but she actually told us to do it this way now.” She just said, “Yeah, I don’t think I have to do that,” and kept doing it the old way. I think it’s really disrespectful that she disregarded me like that but still feels she has the ability to tell me what to do. To me that demonstrates that she feels she’s above me and that mentality is incredibly frustrating to work with.

The worst shift, though, was when I was swamped — juggling the desk, managing the bookings, handling customer queries, all of it — while she stayed locked into this super low-priority admin task. I ended up doing both of our jobs.

At one point, there was something urgent that needed to be done for a client, and I physically couldn’t get to it fast enough (because I was busy doing both of our jobs). She was standing right there, not busy, and instead of helping, she tried to chat. I asked her if she could handle it — and she stormed off.

She did eventually do it, but the attitude was wild. And now I just don’t know what to do.

I want to give her the benefit of the doubt — maybe it’s hard coming back after time away, or maybe she doesn’t realize how things have shifted — but it’s making work stressful. I don’t want to go straight to my boss and come off like I’m being dramatic, but also… how many chances do I give her?

So, am I overreacting by being this frustrated? Should I try to talk to her directly? Keep giving it time? Or is it fair at some point to flag it with my boss?