Answer:
Nell's mom
Explanation:
Let's find the unit rates and compare. I'm going to assume that the more chocolatey one is the one that has a better ratio of chocolate syrup to milk. So,
Nell's mom: 30 mL / 2 oz = 15 mL / 1 oz
Nell's dad: 65 mL / 5 oz = 13 mL / 1 oz