Originally Posted by flyerCO

However to be clear she must be split off and her reservation cancelled before departure. You can't have one passenger in a reservation flying and the other cancelled. It's a simple process to split, so waiting to hope for a change that grants a free refund is best idea. However do need to split it in order to cancel her reservation and remember to do it before departuee. (Even at checkin counter works)

OP, how soon is trip? DL is one of the best/worst (depends how you look at it) when it comes to tweaking their schedules. Anything more then a month out there's great possibility. Less then a month and usually but not always changes are minor. Note a change in operating carrier - (DL to KL for example), including a change in DL Connection operating carrier (Compass to GoJet for example) will allow for a refund.