-if it's a local ride, then carry 1 spare tube, tire boot, 2 tire levers (get the big Pedro levers), CO2, and make sure she knows how to use all these.
-if it's centruy ride or remote, then in addition to the above, carry a patch kit (make sure she knows how to patch), extra CO2 cartridge
-always carry the phone, with a GPS tracking app if you're concerned about her whereabout (GPS tracking drains battery though)