I think you have given her enough chances - no matter what the problem she could have asked a friend to take her to collect the kit if her car had broken down rather than let you down again. In this instance I would refund the deposit and see if the other family you liked still want her. Five weeks is a long time to hold onto a kitten once it has been chosen and gone past its 13 weeks.

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Kaz

For kittens, joy is for the asking and smiles are for the giving