I'm in Australia...also summer here! I just went through this in December albeit with an older bird than yours. If you've taken care of all the basics (regular worm treatment and checking for mites, obvious bloating, ect) you could try some general 'pick-me-ups' like some slightly diluted plain yoghurt (mine gag on the really thick stuff as they tend to bury their faces in the yoghurt, they love it so much), or a calcium and magnesium supplement (I dissolve these in water and mix with crumble very so often).
Do you have Amprolium 200? A very talented chicken woman put me onto the idea of treating for
coccidiosis (
https://www.backyardchickencoops.co...ickens-prevention-symptoms-and-treatment-tips ) when in doubt, especially after a long wet spell. Over the years I've had a couple of girls bounce right back even without other obvious signs of coccidiosis. Water is really hard to keep completely untainted in summer, so treating with Amprolium might be an idea.
Lastly, you can try a bit of aloe juice and a tiny smidge of apple cider vinegar in their water, not enough to put them off, though.
Good luck! I hope she's better soon.
