The coding for this is not difficult, if you are happy for all the LEDs to be the same colour.
If you need something more elaborate, you'll have to explain what you want. Flashy rainbows are do-able. Anything is do-able, really. The main probelm is building something that will allow you to easily enter the sequence that you want. That is - you will get some templates to assemble.
Effects song[] = {
{2, new RGB(0,0,1)}, // 2 seconds green
{3, new FlashyRainbow()}, // 3 seconds oif flashy rainbow
{5.5, new RGB(1,0,0)}, // 5.5 seconds red
//
// and you will have to fill in the rest of these
};
The other main problem is specifying exacly what you want. If you want the lights to flash from mauve to magenta at a tempo of 120BPM and a 1:3 ratio for 15 seconds, sure. But you have to be able to say what you want. I'd caution you against anything too elaborate. It's easy to get carried away and to forget that it's about your daughter, not the super cool gee-whizzery.
An issue might be the stability of the resonator on the arduino. If you rely on that rather than a RTC (which will make the project quite a bit more complex), it may be the case that temperature will throw it off. You'll have to experiment. Cope with the fact that it won't be super accurate - just verse and chorus length.