In my family, we had an unwritten rule - my dad was one of 10 and there were 21 grandchildren. It was decided that once a child turned 16 and was old enough to work, that the aunts and uncles would no longer do the Christmas and birthday presents. So to me, carrying on to 60 SiL or not is incredible! Time to stop the money/gifts bit, especially as it doesn't seem to be appreciated. If it is queried, just say that because you hadn't had a thank you, you didn't think that it had reached her so will not send a cheque through the post in future!