As a jurist she has no experience at all. Nada, zilch, none so she would be mediocre at best.
I can see merit in the argument of appointing someone outside of judges to the Supreme Court to get real-world perspective. After all, the Constitution does not require that an appointee be an attorney or judge.
From what I have read I cannot see Kagan’s career as anything but academic and an insider of politics. She’s a lot like Obama, an academic with no experience for the position she seeks.