To avoid exposing others, I would keep her home from everything (not just gym) until the teammate’s test results are available. If the test is positive, I would keep her home for 14 days from the last date when she was exposed to the teammate, or as long as recommended by local public health authorities.
Gyms, schools, and employers are going to have to get used to people being out for 14-day stretches due to exposure. With exposure at the gym, the owner and coaches could provide on-line conditioning for the exposed groups while they are out. For exposures that occur elsewhere and therefore only affect individual athletes, the gym could put together a 14-day home conditioning program: a list of exercises, recorded videos, and/or links to existing internet videos.