Technically Tom Bradley International Terminal (TBIT) doesn't have a number as it's on the loop between terminals 3 and 4. Note that some international flights do NOT leave from TBIT (i.e., Air New Zealand leaves from T2, Qantas to Sydney leaves from T4 but Qantas to other Aussie cites leaves from TBIT) so please double check her itinerary.

That said, if your mother is going from T3 to TBIT, it's about a five minute walk at a slow pace. No streets to cross, just exit T3, turn right, stay on the sidewalk and you're there.