She had to have found out eventually. She absolutely would have known Lucifer was Rory's dad (who else could it be?) and she'd notice that her sister stopped aging after 20 or so.
As for whether or not everyone can hang out in the afterlife, presumably if Amenadiel was able to send Chloe to hell then he could also arrange for her to pop up into heaven whenever she wanted to see Trixie, Dan, her dad, etc. The show has mentioned that not even God can take a condemned human from hell to heaven, but maybe it's possible to go the other way and it just never happened before because who would