Originally Posted by
Often1
You don't need to split the PNR. Each passenger has a separate ticket. A PNR may have multiple tickets and it sounds as though that is what you have done.
Read the fare rules carefully. Chances are that they will say something such as a $300 penalty for making a change prior to departure and $0 value if a no show. If that is the case, then cancel close to departure. Your friend will still have $100 (in this example) to use within the year.
But, if for some reason, the flight is cancelled or significantly delayed, she may cancel the ticket for a full refund to the original form of payment which sounds like your credit card.
Just a future suggestion as this is a public board, no matter how close a friend, don't book tickets for others. You can help them out by giving them booking information or they can provide your their credit card details. But, in this case it may only be $400, but it could be a lot more - OP is out the cash.
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.