Yeah, this definitely needs to be ruled out. I don't know yet. I told her to try it on her friend's TV (a Samsung; her SNES works fine), her friend's SNES on hers, etc.
I'll let her know the possibility of having to manually select composite input, though that seems strange to me. There have been stranger things, though...
Thanks for the all the comments! Right now she's pretty frustrated (impulsively bought a nice, clean SNES that had been stored in a hard-shell case [possibly for a NES]) but can't play it. I gently encouraged her to go the CRT route, but space is an issue (understandably; I don't miss the bulk of those damn things)