Answer:
The correct sentence is "Smile, Mila! Smile!” When my little sister was almost three years old, she would repeat this every day when I walked in the door from school."
Explanation:
The correct use of tense for these verbs in the context is "repeat" in infinite form and "walk" in the past. The general sentence is in past since it is a memory, the first blank is in a sentence structure with would, whenever we use a modal the verb for is infinitive, then the rest of the sentence is in past form, the subordinated sentence continues with the past structure.
