We have got a wireless Siemens phone system on which one can make internal calls. On this you can either call all the other handsets in the house or choose a particular handset by name. This works from inside the house to the bottom of a longish garden (40-50m).
60m from inside one building to inside another building might be possible - the base station would be in one building and a second handset in the other.
Assuming base station with MIL then she could use it to make external landline calls as well.