My thoughts are along very similar lines .Gives a reason why no Oyster card.I was puzzled why the oystercard was mentioned so much.
NS would not want any bus conductor to look at her too closely.
Also could give explanation why SH travelled to Croydon to meet Tia half way on a journey she had done many times on her own.
Could also be something about the clothes mix up.Tia would have to be dressed in the clothes NS had been wearing .THE woman witness did actually give a correct description of white tshirt
The person the woman witness saw was actually NS returning home.
OMG, are you guys really suggesting this? Do you not have any sympathy for my now liquid brain? I'm going to put my head in the freezer now, hope fully the juices will set beach into a functioning organ! ;-)