middypuss welcome to the QR forum. You might like the QR dashboard and find it useful.
Specifically in regard to transiting DOH my experience is as follows.
In the case of remote gates your wife will be asked if she can manage the 20 odd steps to/from the aircraft.
If she can then she will use the bus and steps like everyone else and be met at/delivered to the terminal door with wheelchair assistance.
If she cannot then she will be met at/delivered to the aircraft door by lift transport.
When answering that question about steps your wife should consider a number of things such as:
Does her disability mean that she is slow on stairs? Does her disability mean that she requires more room to move around (stick, limp etc)?
Especially descending stairs
Will she feel safe descending those stairs with a 'mob' pressing from behind?
Will she slow the disembarcation/embarcation process down?
In other words will using stairs present any safety or comfort issues for her and others?
If she has the SLIGHTEST doubt about steep aircraft stairs then I recommend that she says no and lets the airport transport her in a wheelchair.
There is a little gain for you both because wheelchair passengers and their escorts are NORMALLY exempted transit security checks.