Yes, you could say that she wouldn't have worried. That would be using "to worry" as a verb. The original form is "she wouldn't have been worried" meaning "she wouldn't have been a worried person" and there it's using "worried" as an adjective.

The expression "to be worried" is very common. It has the same meaning as "to worry". In it, "worried" is an adjective (though it has the form of a past participle). So the only verb is "to be", which in the 3rd conditional, becomes "would have been". Here's another example: "If West Ham had beaten Manchester City at the weekend, I would have been delighted."