Timekeeping Issue

Hi all! We have a part time nanny that we share with another family who uses her for the other part of the day. A few months ago, the family changed their hours to an hour later and our nanny never told us. My husband had to ask where she was (our child was at school) because he works from home and she claimed she was here. Anyway after finding out from the other family that she was there and didn’t mention anything we told her to please please communicate and that we wouldn’t be paying her for time that she wasn’t here since she was at her other family.

Fast forward to months later, this happened again but this time I have been home all week. Lateness was 10-15 minutes but when I asked it wasn’t addressed and the timesheet stated starting at the time she wa supposed to be here so I reached out to the other family and again, she changed her hours to stay with them a bit later and nobody let us know.

How do I address this? She has been with us for 1.5 years.