Leasing issue...roomate legality of this?

I just moved into a 2 bedroom apartment hoping that by the end of the year I would have a roommate to help me with the rent...unfortunately it's been difficult finding a roommate. For the Christmas holiday I am planning to return to my hometown...for about a month and one of my good friends needs a place to stay for a while until she gets her living arrangements in order. Without her being put on my 6 month lease, how can she stay in my apartment, pay the half the rent for next month and still have this be legal? (My landlord says that she has to be notified if i have a guest staying more than 3 days).