"Heather's given me the chance to work, where no one else would take me because I have a baby," she says in the video. "She's given me this chance so I can bring my daughter to work with me."
And in the video's final clip, Trumble rails against the press, which Mills has often complained has treated her harshly.
"It drives me mad, these stories that come out. And they're all lies, just so many lies," she says, "and you just want to shout and scream at the press and just tell them that it's just rubbish."
Trumble confirmed to the British newspaper the Telegraph that the video was shot by "one of Heather's team" shortly after she started work for Mills, before adding, "I cannot say any more until I speak to my solicitor."
Dolce, Mills' spokesman, denied that Mills ever had Trumble or any of her employees shoot favorable videos. "It's complete and utter horse s--," he said.
He also denied that Mills had anything to do with the YouTube video.
As for Trumble's allegations, he told ABCNews.com that Mills will respond to the tribunal and that there is "no way she [Trumble] is going to have any case."
Mills has garnered a reputation for being difficult. The judge in her divorce case called her behavior "distinctively distasteful" in his final findings in March.
In September, her former PR rep Michele Elyzabeth told a British paper, "Every time I got her a big offer somehow she'd wreck it or turn down the chance. It drove me mad."
ABCNews.com's Gabriel O'Rorke contributed to this report.