Is it a licensed amateur radio operator, a licensed Citizen's Band radio operator or a bootleg operator of some sort?
Does the bleed-through to your systems contain call letters? An Amateau Radio call sign would begin with a W or a K and maybe another letter before a single number and then two or more letters. There may be an associated vanity vehicle license or window stickers.
The FCC was sloppy in assigning frequencies. The early "color" frequency for TV was actually *inside* a band assigned to amateur radio CW (dah-di-dah-dit stuff) operation. CW schedules where shuffled to avoid the times of the few color TV shows then aired.
The signals may be "splashing" or your TV may have inadequate RF (radio frequency) shielding. A bit or mylar or statigically-placed aluminum foil might do wonders.
If it's the house next door you might get snow problems every time a welder or even a poorly-designed blender was used.
If it's bootleg broadcasting, whether it's interfering or not, if the FCC comes calling the FCC might leave with the bootleg equipment.
Document the time and variety of interference. If you have a VCR, tape it for proof.
Relative to the telephone, the specific method of the telephone installation may be related to the problems. I was once picking up conversation from a law-enforcement safehouse on a hard-wired extention telephone. The length of the wire "tuned" to the portable telephone used at the safehouse. This was mutual fault. Eek! a cel-phone where anyone could snoop the call? They stopped using the cel-phone there.
Back to your mom. If there is no fault in her phone system, there's another reason to complain to the FCC. If she's legally disabled they will be especially concerned.