Imade her other morse code jewelry with dad’s messages — a necklace, an anklet, some dangly earrings, a tiara — but the bracelet was definitely the most beautiful, probably because it was the last, which made it the most precious. explain the ambiguity of the boldfaced text.

Independently of the boldfaced part, there is only one ambiguity in the text.

It is not very clear whether the narrator was talking about the jewelry or the message. The bracelet was the most beautiful because it was the last one made or because it contained the father's last words.

You cannot be sure of which one is "the last" that the narrator is talking about.

It is not clear whether the narrator is talking about the last piece of jewelry he made or the last message his Dad left.

The bracelet was the most beautiful because it was made after practice with the other pieces.

The bracelet was the most beautiful because it represented his dad’s last words.