On 7 hours for the split ticket, I do this often. It is not really 7 hours (as on a misconnect you can not expect to get in at 3:00 AM or such), but is enough to allow for any modest delay on the flight that does not cause a missconnect. The Bangkok Air ticket was cheap, so it a reasonable gamble.

Back on topic, DL is fairly generous on compensation, but I would vastly simplify the story down to the essentials.

Something more in line with :

"Flight XYZ was delayed (MX) significantly causing onward going travel problems and being w/o all luggage for several days. Can DL provide some compensation in the form of SMs for the inconience and DL E-Certs for the expense incurred due to the luggage."

The rest of the story really does not matter, and just clouds the issue.

If you want specific numbers to ask for, there is a good long thread on this issue that should not be hard to find. Go to the FAQ sticky and I think it will be linked there.

I would normally tell your sister and her hubby to save receipts, but that obviously might not be possible. So keep a "diary" to record any purchases made for items that were needed to make up for the lost luggage.

As a side note, another reason why international gogo will be a good thing, they could have emailed or texted the OP hours earlier. With an extra several hours in non-panic mode it would have been a lot easier. True, you would still have endded up in the same predicament, but with a lot less stress.