Hello David,
I am so sorry it has taken me so long to reply to you, many apologies!
The short answer is no, I never did find out any more about Mary. I went to the Archives in Taunton but didnt find anything more.
I think if you reply to this you will have posted twice and so can send me a PM (personal message) and then I will send you anything I have on Mary. She was certainly an interesting lady, but as you say, nearly all the information available is about her life in Australia as a 'First Fleeter' convict.
Best wishes,
Carol