Frontier Airlines EarlyReturns (Pre-Alignment) - Changing Carriers Mid-Itin - What happens to checked bags?

I posted this question (http://www.flyertalk.com/forum/united-mileage-plus/973168-changing-carriers-mid-itin-what-happens-checked-bags.html)over on United, but since the original flight was a F9, I thought I'd post the question here as well.

Our niece arrived this morning, tearful, with no bags. She flew F9 from ABQ-DEN, then UAL DEN-IAD-FRA. She was told her bags would be checked through to UAL, but I found this questionable, because her claim stubs would still be F9 and not linked with UAL. Has anyone had any experience with this? Where should we start trying to track down these bags F9? UAL?

** I did a search for this and was only able to find a post about JetBlue to UAL, but nothing about Frontier.

You need to file a claim with UA. They will fight with f9 for who pays for the delivery.

What did the bags tags show as the final destination? UA and F9 have an interline agreement so they should have been sent over to the DEN-IAD flight.

I will say that interlines (esp. to UA) are low priority and often miss the flight, so I'd bet that its in IAD waiting for the next FRA flight.

I'd start with UA since they were the final carrier, they can trace the bags back through the itinerary. Good Luck!