This link should help:  http://ourworld.compuserve.com/homepages/euraide/over-mad.htm
  I would try to make the reservations several days in advance — particularly for weekends, mid-summer or any event that may involve people traveling on this route.  You will need her passport number to buy a railpass for her and all the name/address type info must exactly match what’s on her passport.  I would suggest some kind of secure shipping as opposed to just mailing it.  Look into buying from a website that ships internationally.   www.railpass.com  and www.eurail.com are two that I know of.  She could also buy the pass in Spain (assuming it’s not a pass for just Spain) but it will cost at least 20% more which is probably more than the international shipping cost.  See “where to buy”  at www.eurail.com
Almost all long distance trains in Spain require reservations which aren’t covered by the railpass and can be fairly expensive.  Here’s a list of reservations requirements and costs (if you buy the reservations in Europe — they’re significantly more expensive to buy from the US). http://www.ricksteves.com/rail/pdfs/07reservations.pdf  However, you’ll pay the cost of these reservations in your ticket price if you don’t use a railpass.  Try www.railsaver.com Follow the “I have a good idea of my itinerary” route and click “I prefer purchasing railpasses ‘only when it saves money’”  Railsaver’s estimates for ticket prices are probably low for Spain — they seem to be pretty accurate elsewhere in Western Europe.  Compare them to the time and cost maps at www.ricksteves.com which are probably on the high side for cost.

Thanks a bunch for the help so far.  From the railsaver website it was saying that buying individual train tickets would end up being about 110 US Dollars, but at another site, RailEurope.com, when I did actual searches it looked like prices would be more like 100 dollars per trip.  Why the big difference? 

  What’s the best way to buy individual train tickets?  How do I get a good price?  Should I ask my girlfriend (already in Spain) to just buy all of our individual train tickets?  I assume buying them at the station in Spain would be cheaper than buying them online here from the states.  Thanks again!

P.S.  We’ll be there during Semana Santa, will that change anything?

The prices for tickets at raileurope.com are what they charge to sell you tickets — including their fees and profit.  It’s usually about 35% higher than what you pay to buy the tickets in Europe.  Same is true for other railpass websites although their prices for tickets may be slightly lower than raileurope.  www.railpass.com is cheaper for tickets but more expensive for reservations. 

You can check prices with the Spanish rail website:  www.renfe.com and buy tickets from them on-line at the same price as buying the tickets in Spain.  However, I’m not sure the website shows all the trains.  There may be cheaper, local trains that don’t show on the website.  If there’s a festival going on, get your tickets early.  Have your girlfriend buy or try www.renfe.com

You could also consider flying using cheap airlines, specially between Barcelona/Granada/Madrid.
It could cost less than 30 euros for one way and much faster.