Mary Elizabeth CHAMBERLAIN was christened* on 10 October 1818 in Great Bentley, Essex to parents named: William & Mary CHAMBERLAIN. (Search Labs)
(as opposed to Mary Elizabeth CHAMBERLAIN who was born 14 May 1815, Winchester, Frederick, Virginia, USA - ref: tree on A##try)
*There will be no Birth Certificate for her - civil birth registration did not begin until mid 1837 in England. There could only possibly be a Parish Record for her - and luckily there does seem to be one (above is a Transcript of by Search Labs). Not all Parish records survive, or were fully kept. Christenings did not always occur near time of birth - sometimes years elapsed before Christenings. But in Mary Elizabeth's case, her age on Census do suggest she was born around the 1818 mark.
The Parish record of her Christening may not give you any more info than the transcript - but you never know: an address, or witness' (godparents) might be recorded and be useful if so..
Cheers
AMBLY