Sometimes it is easy to forget that our nanny/caregiver is an employee. They are trained to the task we hired them for. They are caregivers first and foremost, not housekeepers, dog walkers, gardeners, etc.
You have an employee. The law says she must be treated as an employee.
A nanny (caregiver) should be working the hours specified in the employment contract. If you need her to work overtime, she needs to be paid for the time. Each province has different standards and it is a good practice to check with your provincial authorities.
If you ask your nanny to do anything while she is "off the clock", she is back "on the clock" until she completes the task. Of course, she must be paid for the work. For instance, if your nanny is not working but is at home and you ask her to watch the children while you run to the store... she is on the clock for that amount of time she is watching the children.
A time off is a time off. If you need your nanny (caregiver) to be available "just in case", she is considered working. She is allowed to leave the house during her time off - if you ask her to stay in the house, she is considered working.
Light duty housework such as cooking or light cleaning is acceptable, however doing windows, scrubbing (not sweeping) and waxing floors is generally not acceptable.
These are just some common sense tips that many of us forget when we need that extra hand. Just as you expect to be paid when asked to do something at work, you really can't expect your employee to keep working when they are off without just compensation!