Top 5 maybe. I thnk she would get overpowered quickly by all the harder hitters like Serena, Kvitova or Azarenka. They would just nail her into the backhand corner. Maybe she would adopt a pusher type of style
Whenever I create a char based on a real player, I think about fitting skills. For Steffi it would be Inside Out Master, Poisoned Slices (backhand), and Reach Swings Expert (to compliment her speed and footwork). Of course I could only pick two skills and the only coach with two of them would be Durech, but that guy requires 8 points into S&V which would be atypical of her game. Or you ignore skills a bit and work around stats. Samala for example.
Edit: Fillion has IOM and Diesel Server, might be a good choice.