I think it has to do with the fact that we are describing a skill she has, how well she can do something, so we're kind of speaking in general (thus, not referring to 'now/the moment of speaking'...).... And in such cases in English we'd use the simple present tense.
Hope this helps.
I think the person pronouncing it here uses the z-sound. The ch-sound does not appear in Dutch pronunciation of zwemmen or similar words. Dutch people tend to make the reverse mistake when they pronounce Straße and leave out the ch-sound. It's a giveaway for Germans that a person is Dutch and vice versa.
No, I'm trying to explain why it doesn't sound like swim and what you interpret as a German sch-sound is a actually a z, but with perhaps a somewhat faulty audio. Although many Dutch do pronounce zwemmen as swemmen, like marleinrush noted, it differs quite a bit from region to region. Our w is not like the English w, of course, so perhaps that is why it may sound German to you, either with the s or z pronunciation.
Using the word good as an adverb is nonstandard. That means the majority does not think it is correct, but some people use it that way. I am not sure nonstandard usage will be accepted at Duolingo. In Dutch the word goed can be used as both an adjective and an adverb in the standard language which is why it is taught here.