I went on the 3 night 4 day trek from Cusco to Machu Pichu in 2002. They only allow travelers to go in an organized tour group so the only option is to go with a tour group. I would highly recommend that she take the trek - I wasn't in the best physical state but still enjoyed it immensly. Some may say it is overcrowded but it's all how you look at it - there were quite a few "gringos" like us on the trek but it was still beautiful.
I did not buy a tour package from Canada but bought it locally from Cusco. I paid US$175 for the trek, including a sleeping bag rental through a local agency called "Flamingo" located right in the main square (if you need more details, let me know and I can dig up the details). There are some other agencies that charge more but it should still be cheaper than buying it from here - look at it this way - you are buying it retail from here (like buying a TS from a developer!) while you're buying it wholesale from there (buying it resale!). Our group included five guys (including me, the oldest and 33 at that time!, three Brits and an Austrian) and our tour guide was a girl. We had around 6 porters carrying the tents and other cooking utensils. They made special vegetarian meals for me and I also did not have any problems throughout my 7 weeks travels in Peru, Argentina, Chile and Bolivia.
The price also included one night accomodation in Aguas Calientes, which is the town at the base of Machu Pichu where you take the train to return to Cusco. I strongly suggest that she rest one night in Aguas Calientes. She should be able to get a good night's rest and the morning train journey is better than the evening train as you are able to see the mountains on the way back to Cusco.
One has to apply to go on the trek - the processing time can take anywhere from 2-4 days so I would suggest she do some homework if she's planning on buying local. If she goes with GAP, this may not be an issue but she certainly will end up paying more. I would also recommend strongly that she spend 3-4 days in cusco as it is a beautiful place and ther'e lots to see in the town as well as around it. A few days will also give her some time get acclimatised to the high altitude. Being an Archeologist, she may want to visit the ruins of Ollantaytambo, Sacsayhuman (also known as "sexy woman!" because of the way it sounds), Chinchero and Pisac. These are all within commuting distance from Cusco. I went to Chinchero and Ollantaytambo by local taxis/bus and on the way back to cusco, spent a night in Pisac. From Pisac to Cusco, I took a local bus and got down at the highest point and then walked back to Cusco (around 4 hours) - Sacsayhuman is on the way if you do this. Lonely Planet and other guidebooks (rough guides, etc.) have this info - I used lonely planet.
I am including these sites if they help. I'm sure your daughter will enjoy her trip.
www.latinamerica4less.com
www.go-today.com
Here's a link to a travel agency website that describes the trek (note that the second day is the toughest as you have to climb through the highest elevation on the trek - 4,200 metres or approx 14,000 feet, the dead woman's pass). They list the price as US$300 for the low season
http://www.perutreks.com/inca_trail_04d_itinerary.html
