I'll give you my somewhat dated (~6 years) experience of doing this with a broken foot. I was able to walk with crutches, but the long distances in airports and needing to carry bags, etc. lead me to request wheelchair assistance.

I did YOW-YYZ-SFO and back - I needed to get to the checkin myself (fortunately at YOW this is very close to a door, SFO not too bad either) and from there they provided assistance. But there was a lot of waiting around, I needed to be handed off between different staff (e.g. when going through customers/security for the US in YYZ I was dropped off by someone and then had to wait a long while to get picked up by someone else) and generally I was not a big fan of being on someone else's schedule and being so reliant on others. But everything worked.

I did YOW-YVR-SYD and back right after this and I packed everything in a backpack and did it myself on crutches and by catching rides on carts in the airport. I still had mobility assistance on my BP (so I boarded first, they knew to have a cart at the gate, etc.) but I was considerably less reliant on other people and spent a lot less time waiting around.

I don't know how bad your partners moms injury is, but in summary my experience is that the more self sufficient you can be the better.