Sunburn turned skn Purple

I am not sure if this right place to post this but here goes. Someone I know went to the beach on saturday (5 days ago) and got a pretty bad sunburn. Teh pain is almost gone and the redness is starting to go away but her legs are very purple/blue looking, especially along the borders of the burned area.

She didn't have any major symptoms of sun poisoning, fever, throwing up, etc.

Does anyone know what can cause this? is it dangerouis?

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