very lazy colleague

I work for a small company. Basically a few colleague and one boss no management structure. One of my colleague is very lazy, does all sorts of private things during working hours, no over time. I end up doing loads of overtime and doing her job to make sure it is done. How do I talk to our boss about this? She is very non-confrontational and likes this colleague who was worked in the company longer than me. She is fully aware of my colleague's laziness but so long as I don't say anything is unlikely to react.