They made Chloe because Nickelodeon said Timmy needed a girl foil?
Why not Trixie instead? Give Trixie a Fairly Godparent (a new one, not Timmy’s), show her life as a popular girl who’s secretly a nerdy tomboy. Show her struggling to keep her fairies a secret, especially from Timmy, the boy that she (probably) secretly has a crush on… she couldn’t let anyone know that because she would lose her popularity. Show her conflicting lifestyles; e.g. trying to go to a comic con on the same day as some party.
If they have to change the way the show works to keep it interesting, make Trixie’s wish the B Plot to Timmy’s A Plot. Maybe Trixie’s wishes could be the cause for Timmy’s fairies to lose their wands, or power, or for it to be impossible for Timmy to unwish his wishes. The writers were clearly struggling with this problem of “why can’t Timmy just unwish the wish?” in the later seasons, this would have been a creative way around it. And maybe Trixie and Timmy could team up sometimes, albeit keeping their fairies a secret from each other, or their wishes could keep building on and affecting each other.