Rotoscoping in vegas, can be done quite effectivly, to a point. It has it's limitations, depending on what you want to do. If you just want to rotoscope a mask, that can be done, but if you want to completely redraw each frame, that is a task best suited to other programs. Tell us what you want to do, and I'll try to give you a breakdown on it.
Best to bluescreen it, I'd say. You'd shoot the woman against a bluescreen (a greenscreen would be difficult to key if there are a lot green plants), with plenty of foreground elements (the garden), then you can add in the sky as anything you want.