If your sister has already been issued with a removal order then the interview is going to be about her departing Canada and she may be issued an opportunity to apply for a Pre-Removal Risk Assessment (PRRA). During the interview they will be assessing her continued compliance with any terms and conditions that may exist or that she may become subject to - like reporting in or getting a travel document. It isn't likely that she'll be arrested but one never knows.
PRRA doesn't buy much time and if you don't face any real, objective risk in your home country then they'll knock it off quickly to get the statistic and satisfy the requirement and she will be again right on the threshold for being removed. You can spend all sorts of cash fighting removal, asking for Stays of removal, for example but you have to have very deep pockets for the cash you'll be spending and at the end of the day, you also have to have a reasonable argument for it to be worth anything at all.
I don't know where she's from or what your story is, but people have been trying to wiggle in this way and that when all of the real options have been finally exhausted, and having a refused inland H&C and an existing removal order is really a cue that the final song is being played and it may be time to go home. Pour out the cash and put in the effort if it is life and death, but if it isn't life and death, you are simply further eroding any credibility that she may have remaining should she ever decide to again try and come to Canada.
