Chicken defrosting for over a day?
Your last couple sentences imply the chicken was defrosting in the fridge the entire time?  If so, then the chicken should be fine.  (This is, of course, assuming that the chicken was handled properly before it was frozen, etc.)

Large cuts of meat sometimes take a few days to defrost in the fridge.  (Turkeys can sometimes take a week.)  The only time I'd ever be concerned about a multi-day thaw is if I froze raw meat right as it was about to expire.

In any case, I'd just be sure to use the chicken quickly now that it's thawed.