I think she says something like 読んでこようだ or maybe 呼んでこやった or a lot o possibilities, I'm just a begginner so I can't differentiate exactly what she says, it's too hard for me right now, and even in the subtitles I think her last words didn't got a translation. It is actually something easy to know?
She clearly says:
呼んでこよう is the volitional form of 呼んでくる (呼んで + subsidiary verb 来る).
For 「Volitional + っと」, please refer to this thread: What does volitional form + っと mean?
It sound like you are asking what is said directly after ～と一緒に入る, while she is in the process of standing up.
To me, it sounds like she is saying「呼んでこようっと」, as in 呼んで来る. Which means that she will go to fetch Zakuro-chan.
There are certain utterances that people say when lifting heavy objects, forcing themselves to stand up, etc. (basically grunting). In Japanese these can sometimes take on a highly individualized manner. Some common ones, however, would be 「よいっしょ」and「よっこらしょっと」. I've also heard 「どっこらしょっと」. In other uses, adding っと to the end of a phrase can be a spoken self-motivating tool.
It seems like while in the process of standing up she is saying 「呼んでこよう」while adding the 「っと」in demonstrating the physical exertion utterance or willing herself to action.