My experience with cancellations of non-refundable tickets has been that the entire amount of the ticket will be held by UA until the the itinerary is actually re-booked. That is when the penalty is deducted from the original cost. Therefore, if my experience is typical, when OP cancels, all funds should be held by UA. Then, when the "documentation" is presented, presumably the full amount will be returned.

Also, hope that all works out well for your mom.