Once you've got her signed on for a permanent mission, she'll be eligible for pay increases as usual (unless you decide her bosses hate her or something), so one month of working her permanent job at Minimum before she can get up to Somewhat Decent, then three months working Somewhat Decent, and so on. You would continue to apply for pay increases as usual in the monthly promotions/upgrades posts. No need to mention she's working a permanent mission, unless you would like to!