It would be a lie if Penny said waking up as a baby did not surprise her. She initially believed she had just lost her mind and that it wasn't real. It took her years to accept that this was her reality.
If not for the letter from drunken Penny, she would've forgotten how it was.
Drunken Penny made a lot of sense. From her perspective, if she woke up at this age, she would've carried the habits she picked up while serving time. Back in prison, she was called crazy. So, having a few years as a child gave her plenty of time to rearrange her thoughts instead of doing every little crazy thing she could think of.
However, that didn't mean she was able to help herself. Penny knew she couldn't help herself; at least, she couldn't help the drunken Penny. After all, if she could help herself, then this alter ego wouldn't have existed in the first place.
