It's knit in a DK weight, so you could do this in worsted on a size 10. It's a little stretchy, so you could aim to do it about 2" smaller than your bust measurement, which is what I think she did. It's also a top down raglan and those are extremely easy to make larger. Just keep doing the increases until the back sts measure about half the measurement you need. You can put the sts on scrap yarn, or half of them on another needle, and try it on to make sure it meets at your underarm. I would also suggest casting on 2-3" worth of sts on the body at the underam when you separate off your sleeve sts. That will make the body larger without making the sleeves too big. You have to pick up sts in the cast on ones when you go back to knitting the sleeves, but you can decrease any extra ones on the first round or too, so the arms aren't too floppy.