Looking on the internet deeply has found these results:

She is good in tennis, because while is not is the most popular phrase on the web.

She is good at tennis,because while is not 1111,000,000 results on the web	She is good in tennis, because while is not 1113,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
So she is good at keeping a straight face, and she vigorously crushed any attempt in the House of Lords for the British people to have a referendum. She is good at playing the guitar. She is so good at making people believe she is good with people. She is good at speaking English. But she is good at her job? The manager is good at dodging responsibility. Cyril, miraculously, is good at something, and... Is she there because she is good at her job, or is she there because she is part of a quota?	Dude, you had to play me in tennis, now horse. I mean, no one actually thought he was saying goodbye to tennis for good, because that's a crazy thing to say when retiring. But in tennis, they're forced to interact. She is all that is good in the world. I mean, that's not old, but in tennis, that's old. In tennis, you attack at the point of weakness! Yesterday they didn't play tennis, because it rained. Lettered in tennis, squash, and served as editor of the school newspaper.

She is good at tennis,because while is not

1111,000,000 results on the web

She is good in tennis, because while is not

1113,000,000 results on the web

More popular!

So she is good at keeping a straight face, and she vigorously crushed any attempt in the House of Lords for the British people to have a referendum.
She is good at playing the guitar.
She is so good at making people believe she is good with people.
She is good at speaking English.
But she is good at her job?
The manager is good at dodging responsibility.
Cyril, miraculously, is good at something, and...
Is she there because she is good at her job, or is she there because she is part of a quota?

Dude, you had to play me in tennis, now horse.
I mean, no one actually thought he was saying goodbye to tennis for good, because that's a crazy thing to say when retiring.
But in tennis, they're forced to interact.
She is all that is good in the world.
I mean, that's not old, but in tennis, that's old.
In tennis, you attack at the point of weakness!
Yesterday they didn't play tennis, because it rained.
Lettered in tennis, squash, and served as editor of the school newspaper.