Deeds have been done away with and it is the Registration at the Land Registry which counts now. Your sister is presumably Registered at the Land Registry as Sole Proprietor - to check this if you wish go to
http://www.landregisteronline.gov.uk/ and pay �3 to see and copy the Register. As Sole Proprietor your sister can gift a share to each of you - you have to decide whether you wish to be in a
joint tenancy or a
tenancy in common. The transfer can be a DIY job and you should phone your local District Land Registry Office whom you will find very helpful and will guide you through the process (a couple of forms and around �80 fee). You must also contact the Stamp Duty Land Tax office on 0845 6030135 and tell them what you are doing. They will tell you if there is any Stamp Duty to pay and also arrange for an important Certificate for the Land Registry which they must have before they can do anything.