Poor Douki-chan, she just can't catch a break.

So is she implying that senpai was the one who invited the old friend (maybe out of politeness) or something like "you said no so why is she here anyway".

I'm calling it: she invited herself or follow them to their dat... I mean, reunion.

Pronak said:

I'm calling it: she invited herself or follow them to their dat... I mean, reunion.

Either she (senpai) insist for their reunion, or she insist follow them for promised dinner (he and co-worker), which I presume the latter.

"Oh, you were going to dinner? Perfect, we can celebrate there!"

She absolutely strong-armed her way in there.

Well you know what they say: You snooze, you lose.

It's funny how she's still just "Office Lady" here while the newer rival actually has a named tag.