I am concerned that they didn't have a spaceworthy suit for every member of the crew. I know those suits are hideously expensive, but you need a spare so that if there's an emergency, everyone has a suit to get into. Nobody should die because the only suit that would fit them was in maintenance.
@Andrew Ragland - From what I understand, they never have EVA suits for everyone. If there's a problem, they head to the escape capsules, not EVA suits.
They have the parts for a few suits at all times. They are modular, so changed out as needed for function. As size changes in zero-g (especially continued zero-g) they make allowances for expected changes. She was trained on M/L on the ground, but they thought with the changes in physiology, she'd be L in orbit. They had a M and a L prepped for EVA. She went out in a L prior to this, and though she completed her duties, wasn't comfortable doing so and communicated that. The Mission commander made the assessment to reduce risk to just use someone else that was comfortable in the L for EVA. From a risk standpoint and to keep the astronauts safe, this was the right call.
I doubt they planned to not have a spaceworthy suit available. Though in case of a "The station is holed" emergency, the appropriate response is much more likely to slap a patch over the hole if it's a small hole, or evacuate the holed section fast and seal it off, or in the worst case get everyone into the docked Soyuz or Crew Dragon, rather than for everyone to all start suiting up. Getting into a current-technology space suit takes time. It's not a quick thirty-second change in the airlock. It's not a case of putting the suit on so much as one of assembling it around you.
I'm given to understand SpaceX's prototype suit, as seen on Starman and Ripley, is a lot better in this regard, but it's not human-approved for vacuum yet.