I would have the 5 dates of the days the child was absent listed and then the additional days dck was absent x your half day fee. I always like to put things on paper instead of trying to remember at discussion time. I would use my "gentle reminder" voice with a smile. It could be the client has not kept track and is an honest mistake. Make a copy of the dates and money owed for her to take home. Be confident in your reminder. This is your business and this is your money that is owed. You are already very generous with your clients, so don't back down. Good luck.