From what I've read here and there, she meets him again around chapter 200 of the novel... So theoretically she's still 4 years old (max 5 if her bday is in the middle... But I don't remember them saying anything about that).
I'm not sure if it's a complete reunion or if they'll be separated again tho... so far I've only been able to read almost up to chapter 150 (which is the... third story arc if U start counting from the "armory arc" that's about to begin).
Lil spoiler:
Where I am now she found out his original name... so now she can finally find him anytime >w<. (when it will be possible for her group ofc)

Can someone spoil at what age she reunite with her father? I need to know before I read further, it would be too sad if they only meet again when she's way older T-T