I'm trying to troubleshoot remotely for my mother and her iPad. I sent her a Canon Airprint-compatible printer which is visible/usable on her wireless network by a desktop PC and a netbook, but not visible by the iPad. After trying software updates and power cycling without success, we finally determined that her Actiontec router is not Bonjour compatible. We're about to replace her router, but I thought I'd check to see if there might be a cheaper solution to be found here.
I don't know if it will work, mostly because the product hasn't been released yet but xPrintServer might work. It is a bit pricey for this usage though.
Bonjour is a special form of DNS broadcasting - perhaps if you reset the router to default DNS settings. If you're running multiple subnets for any reason (I doubt so for a 90 year old, but you never know) this will also cause the printer to only be available on one subnet. You'd likely have multiple subnets if you have more than one router.