Many young people nowadays like to go to backpackers hostals.
The cost is around 17 euros per person per night some places may go as low as 15.
Everyone sleeps in a dormitory and it is possible to put possessions into a locker.
You don't have to worry about planning activities because most hostals organise activities such as tapas crawls, guided tours etc.
Within a few minutes of arriving most people are surrounded by a new group of friends and backpackers (usually English speakers under 25)
The reality is that most people end up drinking a fair amount during the evening and for the majority of young people this is a lot of fun. It's a pity this did not exist when I was 20.
It is very important to always use the lockers to put valuable possessions in. If you leave a laptop on your bed don't expect it to be there when you get back.
Another way of travelling very cheaply is couch surfing. (google it)
Good places in Granada are the Oasis, White Heron.
If your daughter would like to have a break from the hectic night life then she could get get an apartment.
There is a special offer in Puerta Real if you pay all up front.
The price can go as low as 20 euros per person per night