The Clover theory is when the last victim alive is a female. This is often called 'The final girl theory'. The last girl left alive is followed by the audience as we experience the remainder of the story through her eyes and it is also her role to either defeat the killer or escape from them. This theory was invented by a women named Carol J Clover and it was widely used in slasher films such as Scream. However this theory has been used in all kinds of horror such as the Alien franchise where the main protagonist Ellen Ripley is almost always the last one alive on the planet/ship that she happens to be stuck on until she escapes, only to find the aliens have followed her into the next film.
here are examples of films where the final person alive from the killing is female.