Sitting all day long, not getting sunlight, not getting exercise, not having any social interactions except with you, and not having orgasms will eventually make her depressed even if she currently does not meet the DSM criteria for depression.

Maybe you can impress on her that you need sex for longevity, if all else has failed?

Benefits of Sex - Health - MensJournal.com (the studies are unclear on causality, so take them with a grain of salt).