IIRC, she is in under a sponser's exemption. She can't actually play in a PGA Tour event because she has not qualified at the PGA Q School (where you go to show you are skilled enough and you get your Tour Card).
However, she has dominated the LPGA in an even greater way than Tiger has dominated the PGA. So, while she hasn't qualified for the PGA Tour, she has shown that if ever a woman could play on the Tour, it would be her. In reality, she's so far ahead of the LPGA, it's like the Suns v. a good college team. Maybe 2 times out of 10 the college kids would win.