Most airlines give a roster to each crew member which lets them know what they are doing for the whole month.
Some airlines let their crew access their roster over the internet by way of a company internet site and by using their staff no. and a password.
Most airlines do give crew some standby duties but not for the whole month. If these standby duties are done at home it is normaly the company that phones the crew member not the other way around.
It sounds an unusual system your girlfriends airline is using.
Hope that helps.