[5.5 spoilers] Sometimes you're just seized by an idea that won't let you sleep until you draw it, regardless of how late it is or how long it'll take you.
The backstory here is that Aisthota found herself with the two problems of "I'm worried about Arenvald" and "my sister won't quit mercenary work even though the literal end of the world is coming probably" and her solution was "I will literally pay my sister to hang out with Arenvald while I do saving the world things"
Rhylgeim was not physically present in Ul'dah when Aisthota decided to go to Limsa Lominsa and become an adventurer, because if she was, she never would've allowed it.