AOG
Actually - the reason that Ms Holliday gave for pulling out is because she had not realised that performing would be (correctly) seen as a political act. She has an absolutely huge following amongst gay people, and performing for Trump/Pence has been perceived very negatively amongst the LBGT community.
Remember...Pence is a supporter of 'conversion therapy', supports businesses being able to discriminate against gay people supports , proposes a cut in HIV prevention funding, opposes marriage equality and voted against the Matthew Shepard and James Byrd Jr. Hate Crimes Prevention Act (which means that straight people are free to beat up and/or kill gay people (specifically because they are gay) in his home state of Indiana without it being recorded as a hate crime.
Ms Holliday's response was:
My only choice must now be to stand with the LGBT community. I sincerely apologise for my lapse of judgement, for being uneducated on the issues that affect every American at this crucial time in history and for causing such dismay and heartbreak to my fans.
With this in mind, it seems reasonable for Jennifer Holliday's gay fans to be appalled at her appearing at the inaugaration.
But the use of the phrase 'Uncle Tom' is reductive and disgusting. Probably used by someone without the education to put the facts before her.