LeAnn Rimes -- the woman who put on the perpetually smiley face after being the other woman in a love triangle involving a married couple -- now says she can't cope with the stress ... and has checked into a treatment center.
A rep for Rimes ... who has spent the past year habitually tweeting out bikini photos of herself ... just released a statement to People.com saying, "LeAnn has voluntarily entered a 30-day in-patient treatment facility to cope with anxiety and stress."
"While there will be speculation regarding her treatment, she is simply there to learn and develop coping mechanisms."
Rimes also issued a statement herself ... saying, "This is just a time for me to emotionally check out for a second and take care of myself and come back in 30 days as the best 30-year-old woman I can be."
"All the things in my life will be there when I get out, but you know what? I'm hoping they're not going to affect me as much ... I'll have the tools to know how to deal with them."