Looking on the internet deeply has found these results:

She is good at tennis, while he is not is the most popular phrase on the web.

She is good in tennis, while he is not 14 results on the web	She is good at tennis, while he is not 1109,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
It doesn't look like this phrase is very popular! The search could not find any examples on the internet.	The Chinese are good at table tennis, aren't they? She's good at tennis too. Perhaps you have mistaken me for my good friend and tennis partner, Wanda Sykes. They know about us: that you're good at tennis, that you... She is good at speaking English. I mean, no one actually thought he was saying goodbye to tennis for good, because that's a crazy thing to say when retiring. I wanted to become good at things, I wanted to become at tennis and school and grades. She is good at playing the guitar.

She is good in tennis, while he is not

14 results on the web

She is good at tennis, while he is not

1109,000,000 results on the web

More popular!

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

The Chinese are good at table tennis, aren't they?
She's good at tennis too.
Perhaps you have mistaken me for my good friend and tennis partner, Wanda Sykes.
They know about us: that you're good at tennis, that you...
She is good at speaking English.
I mean, no one actually thought he was saying goodbye to tennis for good, because that's a crazy thing to say when retiring.
I wanted to become good at things, I wanted to become at tennis and school and grades.
She is good at playing the guitar.