She may hold her breath until she becomes blue in the face. This can be terrifying for the parent as well as the toddler. What actually happens is that the child cries and screams until she has expelled breath so far that for a second she is unable to breathe back in again. If the child goes without air long enough her face will turn a grayish color and she may be close to unconsciousness. Rest assured your child is not in danger of damaging her body in any way.
Reflexes automatically take over forcing air back into the lungs.
Just as each child behaves in an individual way during a tantrum, her needs are also individual. However, all children need to be kept safe. You can accomplish this by holding the child gently, but firmly, wrapping your arms around her with her back against your stomach. In this way you restrain her arms and legs and keep her from hurting herself or others. Some toddlers become more upset when held, so physically restraining these children can sometimes accelerate and extend, the tantrum.