Yes, I see this a few times per week.

The process is very standard. You would contact UA reservations, and you would need to talk to the Detroit Medical desk part, where UA will then get data from her doctor re:flow rates and such. This part is required. Minimum time on this, I believe is48 hours, but most people do it at least 1 week in advance. Prior to your flight (and sometimes a few flights before depending on where the plane is coming from) UA aircraft mechanics board the plane, and install a tank as well as a tune hanging down above the seat. Most planes have only a few seats that they use to, so seat changes may occur.

When you cjeckin at the gate, prior to boarding, ask the CSR to check onboard to make sure that it is already installed or in the process of being installed.

Viola.

Many people feel they need O2, but without the doctor stating so, and giving UA the details, it is something that will not be accomplished. Many people will have a medical supply company provide them O2 in the airport, leaving the tank behind as well. I believe most airports use only a few contractors as the tank cannot be brought onboard.