we lost another chicken

the buff orphington...
egg binding is the only thing i can think of...but this is so odd...
its been quite a while since the astralorp died unexpectedly...so i cant see this being related....but the symptoms were very similar.
this girl was fine yesterday...
today mum goes in the coop and shes in the nest box and mum said seemed to be "having contractions" shed wait for a second then her back would tense and her feathers fluff...this happend for a few mins before she got up and wandered off. about an hour later mum checked on her and she didnt run away when she whent neer her.
i whent out to take a look. unlike the australop she wasnt missing any feathers, she looked lovely, shiney feathers, nice bright wattles and clear eyes,
clean vent.
NO swelling of the vent, no swelling of the rump and no swelling of the abdomen. gave a good feel around couldnt feel any lumps or bumps in there, nothing to suggest anything stuck in the canal, i couldnt feel a bound egg anywhere, an again no swelling at all...
poops been normal as i said, vent was clean.
she wasnt panting, no signs of stress...its a little sticky here today but its not that hot...and none of the other chickens are showing any signs of any of the symptoms...
put her down she kinda half heartedly wandered away, got neer her again and she didnt even try to get away from me, didnt croush, nothing...*sigh*
none of the other chickens are acting odd, they didnt push her out, no injuries no nothing.
mum just whent out to lock them in and she was on the ground under the ramp dead.
i just dont know whats going on...
no signs of paristes or anything like that so i just dont know whats the next step...
i think im going to get a dewormer and a soluable antibiotic and just treat them with both as a just in case...
they get ground eggshell and oyster shell, a layer feed with nothing added and clean fresh water twice a day, theres nothing poisenous in either of the 2 runs...
id think if this was something contageous it wouldnt just hit 1 chicken, then wait a while and hit another, and just hit one at a time with a few weeks between...that would be insane...
the only thing that would make any sense would be egg binding but we havent had any soft shells and as i said, she didnt have any other symptoms, no swelling, no lumps or bumps ect...
this is so frustrating!