Tania (hablar) con mi hermana, cuando yo (entrar).

Hablaba

Entré

Explanation:

Remember that in spanish you have a different conjugation of the verbs depending on the person that is performing the action, in this case Tania, third person, was talking, so the verb would be Hablar, conjugated for thrid person in the imperfect past would be Hablaba, and then the second would be Entrar, in the first person cause it says when I, so that would be entrar in first person in the past: entré.