A 12 year old evacuee is a most interesting concept, and certainly an excellent reason for putting her name into all her possessions.
Furthermore, I never thought that early birth records could be adjusted after the event, so as the short birth cert in the name of Barbara Hilton perfectly corroborates the 2 Dec 1927 birth date used by “Margery A Shaw” it does seem quite acceptable that she may have initially been born and registered as Barbara Hilton, and was then renamed by adoptive parents as Margery A Shaw. It is equally conceivable that as suggested, she reverted to her birth name when she reached 21.
That being so, I have to remain rather skeptical about the marriage of a Hilda Shaw to a Walter C Hilton in 1949, but I am not prepared to dismiss it entirely at present for there may be further supporting evidence. I would need to know far more about the 1949 Shaw to Hilton name change or possibly a name reversal before making that decision.
And I thought this was going to be a quiet and rather uninteresting day before Christmas!
Regards Roy G