It is important to realise that this is a massive gamble of Abigail's. She doesn't know how her supposed "confession" will be received and she doesn't know what kind of power this will give her. Thus it is that in her confession she chooses three people that were already the subject of suspicion by the community. Note how the names are effectively given to Abigail by the Putnams whilst she stands by and watched Tituba being accused and challenged by Hale and Parris. Sarah Good is a name that is mentioned by Putnam and Good Osburn, Mrs. Putnam tells us, was a midwife to a number of her stillborn babies:
Goody Osburn were midwife to me thre times. I begged you, Thomas, did I not? I begged him not to call Osburn because I feared her. My babies always shrivelled in her hands!
Thus Abigail shrewdly picks "safe bets" for her first accusations of witchery. We can cynically see her here beginning to discover the power that such accusations gives her and thinking about how far she can take this power to gain her ends.