She walked out on a joint tenancy after 2 days?

I'm not sure how it works there.In America if both names are on the lease you have to pay your share.I would go to the landlord (if her name is on the lease) and explain that she just took off.See what the options are.Also in america you can take them to small claims and they would have to pay the share of the rent and utilities,if they left without proper notice and without trying to secure a replacement.Good luck and do not let her get away with this.I had a roomate pull the same thing on me a week into the lease she quit her job and decided she was going to move back home.