tax relief when renting in Spain

Hi,

My sister is renting an apartment in Sevilla.  She's 39 and working as an English teacher, with a contract so pays tax.  A couple of her colleagues have mentioned that it's possible to get tax relief on the amount of rent paid to the owner but they don't know any more than that. I told her that declaration this month would be for the year 2009 but she seems to think that there is a new system where you can claim this year for this year's rent so far, probably something to do with making Hacienda aware of undeclared rental. Does anyone know:

a) what is the percentage of tax relief for declaring for the previous year's rental?
b) does anyone know about declaring this year for this year's rental?
c) where does it state this on Hacienda's website (link/http address?)

Many thanks