You can live your whole life in fear if you want, but in my experience, if a girl who is hotter than you are wants to shag, you do it. If you're worried about an STI, learn how to put a condom on correctly, and you should be fine. If she really has only been with 2 people (and both were virgins), the odds of you getting anything are next to 0. However, girls always lie about that kind of stuff, so don't take it entirely at face value.
Asking her to take a test could turn pleasure into business. Don't ask her to take the test. Just sit back, relax, bang her, and enjoy it. You'll be dealing with people later in your life that have slept with 30-40+ people, so you can consider this one the safest you'll ever get. Finally, as Young Jeezy once said:
"Scared Money Don't Make No Money"
Don't be the pussy. That's her job. Good luck boss.