Dear Sis,
It was really nice for DD and DN to get spend so much time together over the days that you and your DH were away in XXXX.
However, there are a few things that I am struggling to understand so thought I would bring them to your attention. I am doing this in a letter as I can then organise my thoughts better and also, because if I try talking to you about them I will probably end up telling you that everything is fine and not to worry about it. But if I don't let you know these things then things will not be fine and I will start to resent having agreed to look after DN this past weekend.
1] I could find no more than 3 nappies in the house when we arrived. I am sure you appreciate that we had to buy some for DN so I have included the receipt.
2] It was surprising to find that there was not enough food, milk and other necessities left in the house. Again, I have included the receipts for the food we had to buy whilst you were away.
The other receipts I have enclosed are for the cost of taking DN XXXX (swimming, to the cafe etc). Again, I am sure you appreciate that we cannot afford to cover these costs but, as the length of your holiday doubled at the last minute it would have been very hard to get by without spending this money in taking care of DN.
We are always happy to help out with DN when we can but I really do feel that you took advantage of me on this occasion. Some advance warning that DN is not sleeping through would have been helpful as the nights we spent at your house were very difficult. DP and I basically ended up working in shifts to cope with her in the early hours of the morning. The fact that the length of the trip doubled at the last minute made it harder for all of us. I guess she was probably unsettled about us looking after her so maybe she's not ready to stay with us for so long yet, even with us decamping to your place to try to make it easier for her.
I am sure you probably just overlooked these things in your excitement to get away and must be feeling very relaxed after your time away. We would like you to reimburse us by the end of the week for the costs we had to cover whilst you were away. By my calculations, the total comes to £XXX.
Thanks - Canyou