My landlady is always keeping me up with loud "gatherings" downstairs. Help!?

I recently started renting a room in a house owned by a 20 year old girl. Recently over the bank holiday weekend she's been having a few people over and making loads of noise downstairs. I would join in if I didn't have to get up for work the next day... The last time I only got 3 hours sleep! I told her to please mind the noise but here I am again, I've been woken up by loud chit chat in the lounge just down the stairs from my room... I don't think she realises how much it stresses me out? What can I do? I pay 300 a month for this cramped room and all I want is a good nights sleep!?