According to Professor Pam Peters, the author of “The Cambridge Guide to English Usage”: “wetted” is used for the past tense when there’s a reference to a deliberate action.
So, I guess it should be “she wetted her hair” and not “she wet her hair.”
Here is what she says in her book:
The choice between wetted and wet for past participle again helps to show whether it’s the product of human intervention, or a more or less natural result:
……..his straight brown hair, freshly wetted and parted in the middle .
The wall had been wet by a broken pipe for many years.
He wetted his lips in a theatrical way.