Interesting to learn of the NZ connection. I think there must be two Rebecca Hambly Pells, as the one I find in NZ who married a Matthew Marriner produced ten children starting in 1838 with John Woon Marriner up to Annie Aubrey Marriner in 1858. My 4x gr aunt Rebecca was born in 1792, which would make this impossible. It is likely therefore that she had a daughter Rebecca born around 1818. You might find her mother Lydia's 1832 will interesting for the witness to it:
I Lydia Hambly of the parish of St Luke Chelsea, County of Middlesex, being of sound mind and memory do make this my last Will and Testament in manner and form following: first to my dear daughter Lydia Martin I bequeath my house No. 8 Peacock Street, Newington Butts, Surry. Also my household furniture and whatever property may be retained in my house No 40 Wellesley Street Chelsea; to my dear daughter Elizabeth Ann Mason I bequeath the sum of two hundred and fifty pounds principle money for her use independent of her husband, the said William Mason to have no control over the same; to my dear daughter Mary Cakebread fifty pounds; my wearing apparel to be divided between my four daughters and all my just debts and funeral expenses and proving this my will to be paid, the residue of stock in my name in the Bank of England to be equally divided between my five children Isaac, Lydia, Elizabeth Ann, Rebecca and Mary and I appoint my oldest daughter Lydia Martin whole and sole Executrix of this my last Will and Testament feeling assured she will most religiously and righteously fulfill the same. As witness my hand this sixth day of October, eighteen hundred and thirty-two.
Lydia Hambly
Witness Thomas Symons, 3 Wellesley Street Chelsea
Richard Woon, 1 Gifford Street, Hoxton