You could hold her, but it would be a long time before we actually awaken her in the game since we're saving her awakening for later arcs in the game. So you'd essentially have to play her as a civilian (who just so happens to have weird deja vu like the other unawakened senshi) until she's awakened. I'm not sure at this point how long it would take before the game got around to awakening Sailor Cosmos, but probably it would be around two months or more. But you're more than welcome to apply for her if that doesn't bother you!