Cyrus, 20, set tongues wagging when she appeared scantily clad while singing two songs -- her hit "We Can't Stop" and a duet with Robin Thicke on his single "Blurred Lines" -- at the MTV Video Music Awards Sunday night.
Cyrus was seen grinding against Thicke in a suggestive manner and making vulgar gestures with a foam finger throughout the performances.
Zap2it.com said Shields talked about Cyrus' sexually charged display as she served as guest co-host of the "Today" show Monday morning.
"I was Hannah Montana's mother. I don't approve," Shields joked, adding: "Where did I go wrong? I'm her dead mother. Maybe that's the problem."
Shields then assumed a more serious tone.
"I just sort of want to know who's advising her, and why it's necessary," Shields said of Cyrus' image change from Disney darling to bad girl.
"I mean the whole finger thing, and the hand, and ... Robin probably at that point was going, 'I don't think this is a good idea.' ... I feel like it's a bit desperate. Are you trying to be Gaga? But Gaga is ... she's got a genius behind all of it, that's not just display," said Shields, an actress and former child model.
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"It's not necessary. It's uncomfortable. And the tongue out, I think it's just a little desperate ... trying so, so hard. ... [Miley] can sing beautifully. And I feel like if she let's that lead, rather than her bottom lead ... ."