Don't see it as gender bias at all - I am not prepared to upset any of my children (girls or boys) on a landmark birthday. I tackle any entitlement issues everyday of the week.
I approached GF parents who had already accepted the invitation at the city venue to try to understand if the issue was crowds, public transport, terrorism etc, ie if it was something we could work around. They were not aware that she had decided not to go and said it was no something specific.
They called me back later to say that she felt unable to go.
We then approached local venues and whilst doing this we had another call from the parents to say that she had changed her mind again and would now come.
We were all delighted with this news and my son was over the moon.
However since then they have not met the deadline for pre-orders, ignored a reminder (my son doesn't know this), so I am no holding my breath.
It has created intense pressure within our family over the past 2 days as we have tried to work out a solution.
So we will see what the evening holds.