[Blunt]

If you want to keep her around just as a FWB, avoid sending any texts about future plans, and definitely don't lead her on with relationship-bait. I say this because you seem like you want to take it easy on her. Try to keep any conversations or invites to hangout to late night (11 p.m. or later), once a week or less, never two nights in a row. Some girls don't have a problem being FWB-status, and doing it this way hints that you don't want a serious involvement without the drama of a direct confrontation.