A likely birth registration for daughter Mary Ann
(Miriam on 1851 census) is Jun qtr 1844 at Bristol, mmn PALMER.
There is a birth registration in Sept qtr 1840 for a Selina PALMER at North Witchford with no mother's maiden name given, which usually means the mother was unmarried. A possibility for daughter Selina?
Though I can't see any marriages for a TRAPNELL and BARRY or PALMER.

You would need to spend some money on certificates I think to see if these are the right birth registrations.
Modified to strike through:
Actually, I don't think that's correct as there is an 8 month old baby Mary Ann TRAPNELL buried at Temple, Bristol on 15 Dec 1844. So still unsure of birth registration for Mary Ann and Selina who were baptised at St Philip and Jacob in 1844 with parents John and Louisa.
Miriam consistently says she was born in Liverpool c1842. I can't see any birth registration or baptism for her.