Thank you everyone for such wondering advice and perspectives!
Millie’s growth chart has been going down since the day I got her, but she has been active and healthy the whole time. Usually she makes slight gains for two days, then drops more than she’s gained in the third day. Today I’m happy to report that it’s the third day of gains! No drop on day three! She’s also back to wanting her hand feedings of formula so I’m breathing a small, cautious sigh of relief lol. Hopefully she manages to maintain or gain some weight back.
Her keel is very prominent with nothing really on either side, but she only just started flying and (hopefully) is going to stop losing weight now and gaining muscle.
Today she is 323g with her lowest weight having gone down to 306g (highest was 361g).
ETA: She doesn’t really eat any other foods. She mouths a lot of things, but isn’t really eating any of it. Have tried pellets (she has access to all day), pellet mush (ran through grinder and mixed with formula), brown rice, green peppers, red peppers, cucumbers, and apples.