[1] Her grandfather Thomas Hallam had been part of the Drury Lane company when he was killed in a dispute with fellow actor Charles Macklin during a performance.

When her parents and William decided to try acting in America in 1752[2] they took three of Isabella's siblings, but she was left in the care of her aunt, Ann, and her husband John Barrington in England.

For most of her childhood except for a few years at school she played small parts in the productions of the Covent Garden company of actors.

Hallam's guardians who she said treated her like true parents opposed the match for reasons that are not certain.

[4] In 1767 she appeared in a revival of Double Falsehood which is a play that claims links to William Shakespeare.