Cider vinegar is acidic (lowering the chance of alkaline crop/gut conditions, bacterial) as well as being a source of nutrients and various beneficial yeasts. Good general health as an occasional supplement. Too much wouldn't be good and may, I think, effect available calcium for egg shells and bones.
Cider vinegar will have no effect on worms whatsoever. The best (only) proper (licenced) wormer for poultry in the UK is Flubenvet.
If she is egg bound, and it has been going on for 3 days, then she will be in serious trouble and I suspect that she would be looking a lot more 'ill' by now (I will be happy to be corrected - I don't think I have ever had a full on case of egg binding - at least nothing that hasn't resolved itself in 24 hours)
If she really does seem to be healthy (i.e. no sign of discharge from beak, nostrils, vent, not 'fluffed up', no external parasites, red comb etc.) then just keeping an eye on her should be sufficient...
but if they have never been wormed - its an absolute must unless you operate a short 'all in, all out' routine. (which I'm guessing, like most here, you don't.)