Ke$ha's friends initially thought she was "getting in shape" and didn't realize she had an eating disorder.

The 'Dirty Love' singer checked into a rehab facility yesterday (03.01.13) for treatment, and relieved friends say they are glad, but admit it took them a while to realize something was wrong.

A source told Hollywoodlife.com: "With her, she is such the life of the party that people didn't notice it and thought she was just getting in shape. And she would hide all the bad stuff from those that are close to her.

"Friends started seeing around Thanksgiving [held on November 28 in 2013] that something was wrong and started talking to her to get help. Thankfully, she took their advice and is getting the help she needs."

Ke$ha is staying at Timberline Knolls near Chicago, the same place Demi Lovato sought treatment for her eating disorder and addiction issues in 2010.

She released a statement yesterday saying: "I'm a crusader for being yourself and loving yourself but I've found it hard to practice.

"I'll be unavailable for the next 30 days, seeking treatment for my eating disorder ... to learn to love myself again. Exactly as I am."