"My older sister is good at swimming."
That's good to know, thanks for sharing!
This site has some more examples helping to differentiate the usage of both nominalizers:
する really means "to do." You can add it to certain nouns to get the equivalent of a verb in English so "let's study" becomes 勉強しましょう or literally, "let's do studying." The "ing" is only added in some English variations because we can use words like "study" as a noun or a verb. In Japanese it's always a noun.
Now, where we have an actual verb in Japanese, we still have situations where we need to use it as a noun (i.e. add "ing") but we do that with の. So 泳ぐ (to swim) becomes 泳ぐの (swimming).