Generally, when a button is pressed on a remote, it simply shorts two PCB traces together.  If you're able to solder, then it would be fairly easy to open the case of a remote, and add two wires which can be run up to the big button on her chair.  Comcast remotes can be bought new on eBay for $6 shipped, and if your cable box is made by Motorola, Scientific Atlanta, or Cisco, the Comcast remote can send the correct signals.   hifi-remote.com/forums/ has a number of threads on opening the case of remotes made by UEI (like Comcast),