Signs of moderate to severe__ include white or grayish skin, blisters, and numbness.

frostbite

Explanation:

Frostbite is literally a piece of frozen skin - usually skin but sometimes beyond - and must be treated carefully to avoid permanent damage. Children are more susceptible than adults because they lose heat faster and because they don't want to stop playing because of the cold. Frostbite makes the skin look white, waxed, numb and hard and may have blisters. It should be treated urgently, preferably by doctors.

In case of frostbite the ideal is to change wet and wet clothes for dry, and go immediately to a hospital. If the feet are affected, the person must be carried. If the person cannot immediately go to the hospital, they should have a hot drink and receive first aid: Put the affected parts in warm water or apply warm compresses for 30 minutes.

you would need to check her bp before and after her activity.