Her parents were Bathsave (born Philpott) and Thomas Newcomen and they were from an influential family with interests in Ireland and the mining of tin.

Her interest seems to predate her marriage in 1647. Letters she exchanged with Abiezer Coppe show that she had ambitions to be, like him, a visionary prophet.

[2] Pendarves was the subject of speculation after Abiezer Coppe, ungraciously, published letters he had exchanged with her in 1649.

[3] Thomasine is seen as holding "deviant views" in a group that included Coppe and John Pordage.

[5] Baptist minister William Kiffin had written to her husband to suggest that he should remove Elizabeth Poole from her pulpit.

Luckily the letter was intercepted by Thomasine who replied to Kiffen telling him that his suggestion was ill-advised and he should in future write to her as she did not trust her husband to act correctly.