My favorite brand of clothing is Donna Karan
Same here, she is such a great American fashion designer for making her brand.
Do you know when she started this designing
Well she graduated in 1966 and went to Parsons School of Design so technically she started designing around then.
It means she has been into this for a long time. No wonder her products are so fascinating 
She really has, since she began working right out of college for Anne Klein.
Did she have any co founder or someone helping her on this
Not that I know of, but Anne Klein seemed to really help her along the way, since she worked for her as an assistant designer.