Hmm..I got a big, comfy cage from Petsmart for my piggies! yes, you should get them in pairs, they're happier that way. I use pine shavings for bedding, I know there is another type of wood that can give them diseases but I can't remember whatis was called. Also, do not get your piggies a raised floor, it can give their feet sores[ouchie!] For food, they get timothey hay[alphalfa works too] guinea pig pellets, and lots of fresh fruit/veggies for vitamin C. They need a lot of vitamin C, or else they can get scurvy. You need to clip their nails about once a month[youmight want your vet to help you? if you cut them too short they bleed] and you need to give them a bath once a month. Use lukewarm water with either baby shampoo orguinea pig shampoo. Anything else is too strong for their skin.
You would need togive them ahouse of some sort[the plastic igloos at petsmart work great] and something wooden to shew on so that their teeth do not overgrow.

http://www.2ndchance.info/guineapigcare.htm - thats a great website for guinea pig care.

guinea pigs are great pets. I hope your daughter likes them, if you end up getting one or two!