Hi, well if she likes to read the kindle app then I think you should already be looking at a phone with a larger screen... So that would start me off thinking of the Droid X. It's an incredible phone and will handle all your mentioned requirements with ease.
If you don't want to spend too much money, have you considered selling her Dare on craigslist to get whatever you can for it? You could also check there for a new phone... some people have brand new ones they are getting rid of for some reason...
I know you didn't ask, but if you are looking at buying her a smartphone... you'll have to pay more. Find out how much Verizon will be charging you for that plan. I was paying $140/mo for my original droid with the everything plan.
If you would consider moving to a different provider, you might get a better deal especially if you are going to be purchasing a new smartphone.
You'll want a phone with good battery life (for mp3's and games), a larger screen for reading the kindle app, and possibly a bigger screen for the touch keyboard, or a physical keyboard.
A great phone would be the Samsung Epic 4G on sprint, it's more of a multimedia phone than anything, with a physical keyboard. It's on Sprint's network... you can check prices on their site. There's always the EVO, my personal favorite, but that's because I own one. T-Mobile also has the myTouch4G and the new HTC HD(Windows Mobile).
I think now is a good opportunity to consider moving on. Verizon is going to be charging a hefty amount for their 4G service... something like $50 for 5GB I think... just becareful, I don't want you over paying, I left Verizon because they were outrageous with pricing.
If youre going to stay on Verizon, I would consider the Droid X or the Fascinate...
hopefully this link will help, not sure if it will work for you
Set Your Location
Good luck and happy shopping.