The cost of providing UM service is very high therefore it doesn't fit with the low cost strategy.
She may just be a year short of being allowed to travel on her own but she is just that - a year short. With any age restriction there is always someone who falls just short.
BA have recently introduced a charge for the UM service. Press release below.
Effective and selling from 01 August 2003, British Airways is introducing a charge for the carriage of Unaccompanied Minors (UMs). This is being implemented in order to contribute to the costs of running the UM service (Skyflyer Solo) which is used by around 150,000 youngsters each year.
From 01 August 2003, bookings for an Unaccompanied Minor to fly with British Airways will be charged a fare supplement of:
NUC50.00/USD50.00 or approximately £32 or Euro47, for a single journey.
NUC100.00/USD100.00 or approximately £64 or Euro94, for a return journey.
The supplement is expressed in neutral units of construction (NUCs) to facilitate the use of a Q surcharge on tickets in different currencies.
Notes:
a) e-Ticket must be used for UMs where it can be applied.
b) Tickets issued for UMs before 01 August 2003 are not subject to the supplement.
c) The supplement is refundable if the booking is cancelled at least 7 days before travel