Answer:
The words that belong in the blanks are: "repeat"... "walked". The introduction should read as follows: “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.
Step-by-step explanation:
The reason behind this is that the modal construction "she would ..." requires a verb that is not in the past tense. Also, the phrase "every day" helps to understand that the first choice should be the verb repeat. In the case of the second blank, "when I..." requires a verb in past because it refers to an action that took place in the past "when my little sister was almost three years old."