Zoe is kinda depressing thinking about it now
Listening to her voice line she has one where she say's "I wanna have fun and chat with someone besides myself". This considered it seems like if she is only a herald to more powerful entities whoever her bosses are brush her off until she has to do her job and if that is the case her entering Runterra might be the most exciting thing she's gotten to do. Considering her personality she seems really desperate to make new friends and impress everyone because this may be the first time in a long time that she's gotten to interact with anyone. This explains why she's so thirsty for Ezreal and why whenever she interact with a female champ she wants them to be her BFF or sister so she can have someone to relate to.
Also everyone complaining she's very immature despite being as old as she is, she might still be a child by immortal standards. Like from a mortals perspective she's ancient but from an immortals she's practically still a young girl at best, that or she's manipulating her age with abilities idk lol .....