You should count yourself lucky that your wife is able to express her pleasure in dirty words. It means that she is open during such times and wants you to reciprocate with action when she names those body parts that we say are bad words.
At such times you should also join in with some of your own choice words, so that will relax her. As long as the dirty talk does not offend you such as incest relationships, you should go along. Talking dirty reflects the level of comfort that you partner shares with you. It will rarely happen if there is no chemistry between partners.
Talking dirty can be low rhythmic grunts, high pitched squeals or whispers. It may not even be words.
One point to remember, never to bring up this topic at other times. She shouls not feel that you are laughing at her or mocking her. So do not repeat her words during normal times.