Lena Headey is indeed the voice actor for Patty in Risen 1. If the name doesn’t ring a bell, know that she is playing Cersei Lannister in Game of Thrones.
Check out her Imdb page and search for “risen”.
I was replaying Risen 1 as a mage and noticed Patty’s voice. Since Risen 1 was released in 2009 and Game of Thrones in 2011, I guess many gamers didn’t knew about her.
Patty from Risen 2 has a different voice actor though.