"Hello, Alexis, welcome to ELU." In the sentence I just typed, I am addressing you (Alexis) directly. That is referred to as direct address, which is offset by commas when in the middle of a sentence. (See rules in link below.)
So, the placement of commas in the first sentence...
Hey, pretty lady, you seem like fun.
...before and after the direct address ("pretty lady") is correct.
Always use a comma when directly addressing someone/something,
regardless of whether the direct address is at the beginning or end of
the sentence. If the direct address is in the middle of a sentence,
use a pair of commas to set off the direct address.
That being said, leaving commas out of greetings (with direct addresses in them) seems to be a common error that is, perhaps, becoming more prevalent.
Hey, honey, pass the honey.
This chair goes over there, sweetie.
Would you like a chocolate bar, little one?
“Hey, buddy, pass the chicken.”
“I’m distracting you, little turd blossom.”
“Hey, dude, check out that chick.”
“Hand over that phone, jerk!”
See #7: https://dianetibert.com/2015/03/09/when-to-capitalize-names-that-are-not-names/.
Some examples aren't so endearing. See more examples in the link below. Have a nice day.