If she is interested in the Prius, the federal tax break has been phased out because Toyota has sold over 60,000 units of hybrid vehicles (after that number, the tax break for hybrids made by a particular car manufacturer gets phased out, as is currently happening for Honda. See the chart in the link provided.)
http://www.irs.gov/irs/article/0,,id=176409,00.html
Depending on your state, there may be some sort of state tax break.
Some general info for shopping for hybrids and other fuel-efficient/alternative fuel vehicles:
http://www.hybridcars.com/shop-by-technology