The really funny thing about this decision, for me at least, is that's my canon Warden. But this was probably not the reason they picked it. So, why do you think a Dalish female is the default Warden unless your past games say otherwise?
My hunch is that it's because she lost the most in her origin. After all, Tamlan, as a ghoul, revealed he had always loved her. And I bet he was planning on proposing to her that evening. So had fate been kinder, she would have had a husband, and a family of her own. She would have had a happy and normal Dalish life. And now that's all gone. If a Dalish female was your canon Warden, would she accept a proposal from Tamlan if fate was kinder that day?
Why do you think Dalish female was made default?