The 43-year-old star announced in August that she was going to enter a clinic to receive treatment for Post-Traumatic Stress Disorder (PTSD) following the death of her father and the breakdown of her marriage to film producer Stephen Belafonte.
The 45-year-old model is on the 'America's Got Talent' panel with Mel, and she thinks the Spice Girls star seems to be coping despite the circumstances.
She told 'Entertainment Tonight': ''To me, she seems [to be] doing really well.
''Yeah, spirit is up. She's excited to come to work. We're having a good time together. I think she's good.''
Heidi's update on Mel came after the show's boss Simon Cowell, 58, said the 'Viva Forever' hitmaker has given 'AGT' her ''total focus'' despite her problems.
He said: ''When you go through this job for a living and crazy, crazy things happen around you all the time . . . one thing about Mel is that she comes on this show with total focus.
''She isn't complaining or moaning, she is all about the talent - that is all she talks about. Not herself, and that is hard.
''So I give her a few nods for that.''
Earlier this month, Mel was ordered by the court to submit four months of drug and alcohol testing after a judge demanded a ''full scale evaluation'' as part of her custody agreement for her's and Stephen's daughter Madison, seven.
The singer is determined to prove she's a fit person to look after her children and has agreed to do a drugs test twice a week instead of once.
Her spokesperson Gary Madatyan said: ''Melanie is willing to do whatever it takes to provide proof to the court that she is a stable person.
''She was ordered to take one test a week, but Melanie wanted to do more, and offered to do it twice a week. Melanie will be drug tested twice a week.''
However, Mel had clarified she didn't need help with alcohol or sex addiction after rumours began to circulate.
She said: ''I've been in therapy since my father got diagnosed with cancer nine years ago. My therapy changed a little bit because I was in a very intense relationship, which you can all read about in my book.
''I do address a lot of those issues. But you know, no, I'm not an alcoholic. No, I'm not a sex addict. You know, I was with the same person for 10 years and that was quite a turmoil, very intense. That's all I can say about it.''
Mel also has daughters Phoenix, 19, and Angel, 11, from previous relationships.
His new album Underneath It All is out now.
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