She is voiced by Cherami Leigh in the dub. Try to match this voice.
https://youtu.be/L2XMT2OiJh0?t=1m11s

Patty is mostly seen speaking in a sing-song voice, as she often says '♪' after her main speech. She acts and speaks like a young child. She pronounces words like "hello" and "sorry", as a child would "hullo" and "sowwy", and seems to still be learning about simple things such as assigning animal noises to the right animal. She is certainly unaware of more complex concepts, such as those of genders other than simply male and female. However, these may not have been explained to her due to her generally childish demeanor and inability to understand a lot of things, as exemplified by Liz congratulating her on simply getting animal names right. This lack of knowledge may be due to her growing up on the streets and presumably not having a formal education.