In terms of her instantly removing her spacesuit, as well as the psychological desire to get the hell out of what nearly became her tomb the suits on the ISS in the film seemed to be of a different design to the one she was wearing, if the air tanks* weren't compatible she'd have had to take the one off for the other at some point anyway (or if they are the same, would it be easier to just strip and put a fresh suit on rather than fiddle about trying to change her own air tank?).
*Possibly not the right term...
I agree, it's entirely plausible that she'd have to change suits, eventually.
However, I think that the de-suiting scene shows her acting in a way that isn't optimal (I think it would be more optimal to wait until actually getting a new spacesuit), although it's for the sake of advancing the rebirth theme, as Gaith
put it, and which you also seem to be picking up on there ("get the hell out of what nearly became her tomb"). Furthermore, choosing to de-suit then and in that way defines her character. All of that is more than perfectly fine in film, and so that's not a negative criticism I'm making here.
Almost losing her tool was also not optimal, it defines her character, and I'm certainly not faulting the film for putting that in.