How is on-call time paid?

1) For the time she is actually on-site or in the facility, she must be paid--that's clearly work time.

2) For when she is on-call, IF she has to stay on-site or in some other location the employer specifies, that, too, is work time, and she must be paid. If on the other hand she is free to do what she wants as long as she is reachable by cell phone or pager and prepared to come in, then until and unless she gets the call, she is not working and does not need to be paid.

3)  If she is an hourly employee, then she will only be paid for hours actually working.