At age nineteen, Sinclair attended a performance of The Gladiator, starring the popular American actor, Edwin Forrest, as Spartacus.

The literati discussed such works as George Sand's novel,Consuelo, which proved fateful to the Forrests' marriage.

While on tour in Cincinnati, Forrest left his wife in the company of Jamieson while running an errand.

Apparently suspicious, he returned ahead of schedule and encountered Jamieson performing an amateur phrenological study of Mrs. Forrest's head.

According to Mrs. Forrest, who defended the novel, she had challenged Jamieson to write a love letter that rivaled Mrs.

Forrest, represented by John Van Buren, accused his wife of scandalous and immoral behavior with several men, including Jamieson and the poet Nathaniel Parker Willis, who was named as a co-respondent in the case.

[1] On February 22, 1852, Sinclair appeared as Lady Teazle in School for Scandal at Brougham's Lyceum Theatre in New York.

In San Francisco, she appeared as Katherine opposite Edwin Booth's Petruchio in The Taming of the Shrew.

Sinclair is reported to have worn a French gown worth $1200 ($19 was considered extravagant for a costume at that time).

[6] By Christmas, she became one of the few female actress managers by leasing the Metropolitan Theatre, "a very grand house against which smelly little San Francisco Hall couldn't hope to compete.

"[5] She opened on Christmas Eve with School for Scandal and hired Edwin Booth for juvenile leads and the rising star Laura Keene to play opposite him.

[5] Sinclair's Metropolitan Theatre, which she called the "most magnificent temple of histrionic art in America,"[2] offered melodramas, burlesques, and romances starring the famous actors of the day.

Her reviews lauded her physical beauty and stage presence, but her main attraction seems to have been her status as the former Mrs. Forrest.