It seems it’s in the ‘base’ model. As I came up with the ‘(a girl)’ part I’ve had something immortalized in a Chinese AI model. I suppose.

Without the prompt dolphin uses, I get his (using rep pen 1.1, not sure why that affects it)

Sally (a girl) has 3 brothers. Each brother has 2 sisters. How many sisters does Sally have?

The answer is Sally has 1 sister.

Here’s the reasoning:

1. Sally has 3 brothers.
2. Each of her brothers has 2 sisters.
3. So, each of her brothers has the same 2 sisters.
4. Therefore, there are only 2 sisters in total (not 4).
5. Since Sally is one of those sisters, she has just 1 sister left.

That’s it! The answer is that Sally has 1 sister.