the one thing, the only thing

[diamondcutter]

Andrea takes classes in everything. She probably even takes a class in how to be annoying, because that’s the one thing she’s good at.
Source: My Weird School 14, Miss Holly Is Too Jolly, Dan Gutman

That’s the one thing she’s good at.

Does this sentence here mean #1 or #2?
1. That’s one of the things she’s good at.
2. That’s the only thing she’s good at.

 

[emsr2d2]

The use of "the one thing" means it's the only thing.

It's one thing she's good at = She's good at other things too.
It's the one thing she's good at = It's the only thing she's good at.

 

[diamondcutter]

Can we also take “That’s the one thing she’s good at” here to mean “That’s the thing she’s best at”?

 

[5jj]

No. That would imply that there were other things she might be good at, merely not so good.