Think may of possibly found it.

An Arthur HAMLYN marries a Elizabeth Ann STENLAKE in Antony, Cornwall 28 Sep 1835.
Occupation given as Plasterer, same as occupation for your Arthur on 1841 Census assuming I have found correct one.

Also on the 1841 Census in same house is an Ann Westcott, of right age to be Elizabeth's Mother.

There is a marriage of a James WESTCOTT to an Elizabeth STANLAKE 22 June 1814 in St Andrews, Plymouth.

So therefore would assume that Elizabeth is possibly the illegitimate daughter of Ann STA(E)NLAKE who married James WESTCOTT.