Since the body cage of living cables only had limited suppression, the geniuses at the lab came up with a clever device. It distorts time space, making her muscular expansion take up less space than it's mass would actually reflect. For every square inch of mass you see, is actually a square foot. Working out pushes it's limits, but it's this and a host of other devices that allow her to look "normal" to the outside world.
And she's still growing.