I would not advise Fedora as the latest ones can be a bit heavy on install. I always like Elive if it is for some one who has a slow machine but likes eye candy. It has pretties and ran well on my old 450. Not to mention elive is VERY user friendly.
If there is no preference on the eye candy there is always damn small linux (another fav of mine) there is a version that uses XFCE and is pretty light but balances the needs of a new linux user pretty well.
Debain would not be bad either. I ran KDE on my PII 450 lappy for a while. It was a little slow on boot but once running I had no issues.
I second that about ELIVE
I've used ELIVE englightenment environment for over a year and I occassionally run it once in a while. Eye candy is a "MUST" for young people ! We prefer eye-candiness over anything else.
on the side note, I'm using Mandriva2009 at the moment, with unbelievably supersweetness of Compiz-Fusion + the extra rotating cylinder instead of rotating cube. But it would be for newer and faster computers.
but back to the original topic.. pentium2 and for a very very young person ( I assume 8 - 10 yo), I would say XFCE if she's been exposed to winXP, ELIVE if she's been exposed to winXP or MAC.
However.. this might also worth trying...... it look super super simple for an 8 y.o...a Google's OS !!