The star has reportedly threatened to quit the hit E4 reality show, after producers pressured her to film scenes about her upcoming wedding to Professor Green.
Millie - who is currently planning her September nuptials, after the rapper proposed last month - has apparently refused to have any of the preparations or the ceremony itself captured for the show, angering bosses.
A cast member, who refused to name themselves, told The Mail On Sunday: "She is depriving the show of a very strong plotline. Apart from on one or two occasions she has refused even to allow Professor Green's name to be mentioned.
"Millie hates 'Made in Chelsea' now. The producers keep pressuring her to let them film her wedding preparations - and the wedding itself - but she wants to keep it private."
They added: "Either she lets the cameras into her preparations or she won't be able to stay on. Professor Green doesn't want to be on the show and neither of them wants TV crews anywhere near their wedding.
"It looks as if Millie is ready to move on from the show entirely. If she's not having any fun, then there's no point for her."
It isn't the first time she has angered her castmates with her attitude towards the show.
He said: “Millie is with Professor Green, who isn’t on the show, so what is being covered?
“She is just getting involved in everyone else’s business... it’s just like, ‘No one really gives a f*** what you think’. Millie is the show pony, I have nothing nice to say about her.”
His comments prompted Professor Green - real name Stephen Manderson - to explode on Twitter, calling Spencer a "silly pompous jumped-up c***", warning him not to "utter a f***ing word about our engagement".