Actually, we humans should be eliminating 2-3 times a day. Most of us, however, are not that lucky.
Laxative abuse as a form of weight control is a known disorder and can have some serious long-term effects. I do hope you can gently express your concerns to your friend regarding her well-being and encourage her to find more reasonable methods of managing her weight. If chronic constipation is an issue for her without the laxatives, she may need help from a health care provider who can recommend diet/lifestyle changes or other less drastic means to keep herself regular.
Best of health to you both!