Answer: Selena started playing hockey, her favorite sport when she was seven because her older sister was a star goalie.
It's not the first one because there shouldn't be a comma after Selena since it's separating the subject (Selena) and the verb (started). It's most likely not the last two either because there's a comma before the dependent clauses ("when" and "because"). Since these are all complex sentences, they're made up of one independent clause and at least one dependent clause. Since the dependent clause follows the independent clause, no comma is needed after it.
You can even read the sentences out loud with the appropriate pauses at the commas to see which one makes more sense and flows better.