Hi
I believe she was born on 28 April 1801 and baptised on 10 May 1801 in Liverpool according to LDS. Her parents are given as David and Ellen Rowlands. I think she had a brother George born 18 July 1803 and his parents are given as David Rowlands and Ellen Griffiths.
I have found a Richard Griffiths marrying an Esther Pemberton in All Saints Liverpool on 29 July 1733. I think this could be her grandparents as the date is too early for parents.
The names Rowland, Griffith and Pemberton all appear as christian names in Mary Ann's children or grandchildren making me think this could well be the correct family.
It's Mary Ann's parents who are proving difficult! I've found a David Rowlands' death in Liverpool 2 quarter 1844 BMD 20 269 and an Ellen Rowlands' death Liverpool 1846 3rd quarter 20 269, but can't find them in the 1841 census.
Thanks
Jan