Which character should tell the story?

As I see it, you have two choices. The simplest is to create another character, perhaps a sidekick that sticks with Girl 1 and when she dies transfers her allegiance to Girl 2, Look at the Sherlock Holmes stories, for example, to see how a secondary character narrator can be effective. That can also give you some ways to hold tension since the narrator doesn't always know everything the protagonist knows. The second way would be to have Girl 1 be the narrator up to her death then end that chapter there and start a new chapter with Girl2 as the narrator. That way is a little trickier to handle but could work. I think you should choose the first way and write a chapter each way it and see how that feels. If you choose to change POV, try writing the first chapter that would be each protagonist's and see how that feels. Either way, stick with it and get it done. To be a successful writer takes talent, luck and determination but if you have enough of the latter, you only need one of the first two.