I think it is the fact that KG is a mature player who has presumably demonstrated all that she will be in the WNBA, whereas Kelly is a developing player at that level with some significant remaining upside, that caused the Sun to keep Kelly over KG. I don't think KG's frienship with Tina had anything to do with it (the same applies to Renee Montgomery).
Kelly apparently had a tough year overseas, first recovering from the injury in the last ND game and then with illness. Her jump shot does not look as if it has recovered the accuracy that it had in her senior year. If it does, then she will be an adequate offensive player even in the WNBA.
There is redemption for these kinds of players in the WNBA. Allie Hightower was a bit player in her rookie year and was an all-star last year. Allie Quigley (who I hope will forgive my disparaging comments about her a few days ago) now appears to be Chicago's first guard off the bench at least until Prince returns -- finally, in her 6th year, after barely appearing in games in her first several seasons.
It seems that this board is eager to give up on Kelly, which I find hard to believe after watching her for four years. I think posters here are also eager to give up on Ann Donovan, although I agree that her career as the Sun's head coach is on thinner ice than Kelly's. (If the Sun start out 5-12 or worse, she will be gone in mid-year, as would be appropriate.) But I certainly remember many posters disparaging Thibault when he failed to win a championship, and a few calling for his head before the Sun in fact axed him. Of course, none of those posters has to be accountable for those recommendations -- that's why they (i.e., we) are just posters and not basketball executives.