Adult ages in the 1841 can vary by + - 5 years due to the rounding that was "suggested " that the enumerators followed. Not all did !

So most adults are aged 25,30,35,40 etc !

PARNACOTT, PARNECOTT, PARNACOTE, PARNICOTE etc exists in Devon and Somerset; PARNACOTT hamlet is near Chilsworthy, and Holsworthy North Devon

In a later census 1871 ? Mary is described as from Somerset. so that may be where she was originally from.