"She does exercises."
Translation:Sie macht Übungen.
If it's as a sport, e.g. push-ups, I'd suggest "Sie trainiert" ("she works out"). If it refers to e.g. math homework, I'd suggest "Sie macht (or even: löst = solves) Aufgaben" (literally: "she does tasks"). If it's a Duolingo course, I'd go with Glutexo: "Sie übt" ("she practises").
"Sie macht Übungen" is correct for all the above, too. In reality I guess you'll hear that phrase more likely in a specified context: "Sie macht Stimmübungen" (vocal exercises), for example, or "Konzentrationsübungen" (to focus better)... (...but there's not a lot of words where that works out. I suppose it works when using the purpose of the exercise, not the "means"/object. Like, "Fahrradübungen" / "she's pracising how to ride her bike" would be wrong. That would be "Sie übt Fahrradfahren", provided she's still learning how to do it. Otherwise, if she just does it to stay fit or is training for a competition, then "sie trainiert".)