1000 calories a day isn't much, so it's going to take a while at this rate.
Here's how things exactly work. Every character has a calories threshold they need to reach before they start gaining weight. For NPCs, this threshold is a bit lower than for playable characters, so assuming Emma is at her minimum weight, it shouldn't be any more than 500cal.
Then, once this threshold has been reached, any calories above the threshold will contribute to weight gain. The conversion rate is 3000cal = 1 kg.
So if you feed Emma 1000cal a day, she'll gain less than 200 grams every day, so 2.8kg in two weeks. That won't be noticeable.