Hi amitygirl,
The first place I would start your research is the tutorial post here which has the basic information, steps, and guidelines that can help you make the best possible purchase for your daughter.
The tutorial also includes a link to a list of several of the better retailers and manufacturers that sell memory foam mattresses online and some of these may sell a mattress that is a reasonable approximation to the iComfort insight (which is a fairly basic mattress with about 2" of gel memory foam over a firmer support core which is similar to many of the more basic online mattresses).
If you let me know your city or zip code I’d also be happy to let you know of any local options or possibilities I’m aware of in case you are more comfortable purchasing a mattress locally that your daughter can test first.
Phoenix