Update on this - The first leg of our flight to AMS was canceled due to Storm Darragh, but Delta rebooked us through Boston, and we ended up on the same flight into OMA. So it worked out fine in the end.

That said, the app never worked. It told me we couldn’t check in because we “didn’t have an electronic ticket”—which we clearly did. I called Delta, and while the agent was very nice, he couldn’t help and suggested checking in at the airport. They did check us in, but by the time we got to the gate, we were "unchecked in" (the gate agent’s words).

Thankfully, in Dublin, the check-in agent, who was also the gate agent, upgraded us to Delta One, I suspect more out of an operations upgrade need versus because of our hassles. However, when we got to Boston, the BOS-DTW leg didn’t have us on the upgrade list, even though the online record said we were. Neither calling Delta, nor speaking with the Sky Club agent or gate agent, fixed it. They were baffled....

Bottom line: It all worked out, we got where we needed to be (with a TATL upgrade and everyone I spoke to at Delta was really nice, they tried to be helpful but the tech really let us down. It sucks. Also my daughter's login issues never got resolved.