We all have different opinions and different ways of parenting/grand parenting.
KA works for her money, good on her.
Having flown BA Club, all that separates you is a curtain, she could have back row club, they could have front row economy, I honestly cannot see the problem.
Our children always sat in a row together, Husband and I normally in front of them, so if they kicked seat/played with tray table it was us they annoyed.
I think she is being attacked unfairly for doing something that deep down and if financially able, lots of people would have done.
My AC think this is hilarious, and waiting for GC to reach teenage years so they can sit away from them on the plane, for a couple of hours of relaxation after the pre-holiday stress and the coming 14 days of holiday mayhem!! I must add that they are exceptionally good and know how to behave.
My eldest GC 16 has been flying backwards and forwards to Europe as an unaccompanied minor for years, and on reaching 13 has flown happily and confidently on her own, without assistance.