PSP hands down kate. I had both. Still have my PSP in fact two of them.
Um no.
First of all, I have not seen a female that has been happy with the PSP, unless they use it for movies.
I currently own both a PSP and 2 DS Lites, and 2 regular DS's. The game selection on the DS is so much better than the PSP it is beyond silly. The fact that you can play Gameboy Advance games on the DS, and it is $129, vs. $199 to start off with, and the choice should be a no-brainer.
I am not sure if you do, but if you look at all of the highest rated games on the PSP, almost all of them are direct ports from the PS2. The DS has so many games that are unique to its system alone.
If you enjoy watching movies on the PSP, that would be the ONLY reason that I could recommend the PSP right now. The lack of titles (even this late in its production cycle) is downright alarming. I honestly believe that you will enjoy the DS Lite over the PSP. With the $70 you save, you can buy 2-5 games and still be ahead, as you don't have to buy any memory cards with the DS Lite.