No wheelchairs at the hotel, but you can rent one in the parks or you can rent from an outside agency for the time you will be there. Just do a google search for Orlando wheelchair rental and you can get prices for your stay. You can also give universal a call and ask for current daily w/c rentals. Depending on how long your stay will be, it may be around the same price to rent per day at the park, and it sounds like your mom gets along fine most of the time, so the walk from the parks to the boat ramp is pretty short, so maybe you would not need the w/c for that part.
Since you have express pass and will presumably be using the express lines, just ask the team member outside the express line and ask them what you need to do.
As damo said, the lines are set up for w/c. but by asking the team member what you need to do, you may be shown in thru another way.