Please help! Girl Trouble!?

hi im 14 and theres this one girl at my pool that i realy wanna try talking to. I've never talked to her and i'm not sure how to approach her. Normally she's sittin with her mom and i guess her sister. She goes in the pool rarely but its normally with her sister. Im not sure how i should approach her or what i should do. I also sometimes have trouble talking to girls that im not good friends with.