Once Ochaco uses her Quirk to negate the gravitational pull on an object, she can press the tips of her fingers together to release the effect. Using it on multiple objects at a time or overusing this technique greatly exhausts Ochaco, even to the point of vomiting.
However, she appears to have gained a greater level of tolerance to the repercussions. During the U.A. Sports Festival, Ochaco is able to release an entire arena's worth of debris on Katsuki Bakugo and still continue on fighting afterwards.