Depending on which gate the incoming flight is, it's also potentially a long walk to the transit security checkpoint as well if it arrives at the far ends of the terminal. If you imagine TPE as an "H" shape, transit security is in the crossbar of the H. One on each side of the crossbar for both T1 and T2.
I haven't availed myself of the service, but I've observed very attentive wheelchair assistance if you wish to ask for it for your friend.