updated 09/04/2012 AT 6:00 PM ET
•originally published 09/05/2012 AT 3:00 PM ET
“She’s already feeling better, stronger,” a friend of the country star tells PEOPLE in its new issue.
Rimes voluntarily entered an undisclosed facility the day after her 30th birthday “to learn and develop coping mechanisms,” her rep confirmed last week.
“I’m happy and healthy. I just want to be happier and healthier more consistently,” Rimes told PEOPLE before she checked into treatment. “I don’t want to wake up and not truly be enjoying my life and these amazing things around me.”
Rimes – who is married to actor Eddie Cibrian and has been gearing up for the release of her latest studio album Spitfire – is expected to temporarily leave treatment for a trio of long-planned Midwest concert dates this weekend before returning to the 30-day program.
Since she launched her career as a child, “I’ve been built up and torn down, built up and torn down,” she tells PEOPLE. “It’s been difficult to tune people out, especially in the last few years.”
For more on Rimes’s reasons for seeking treatment – including her hopes to expand her family – pick up this week’s issue of PEOPLE, on newsstands Friday