Not sure where you are having baby but RWH have child care facilities but i am not quite sure where you stand when it comes to labour as they do recommend to book in advance when it comes to normal appointments etc.

I second what has been said about finding FDC or getting little girl into childcare and hopefully developing a relationship with one of the carers and getting them to help out and be on call for the birth.
The other options would be to take her with you, and I don't think that is a necessarily bad idea but you would need to be well planned with how to entertain her while you are there! And probably talk about it well in advance to prepare her. DS has a leapster game thing that he loves so if we end up having to take him it should keep him entertained That and we are also (barring any committment that means she cannot attend) having a student midwife so we will have an extra support.