No. Because this is using a superlative ...y fwya plentynnaidd we use an emphatic pattern with hi (the one who is the most whatever) being put put at the start if the sentence:
- Hi yw'r dala - She is the tallest
- Owen yw'r byrra - Owen is the shortest
- Y dyn 'na ydy'r cyflyma - That man is the fastest
Yes, unless there is some specific reason to use another pattern.
See the explanation and examples in the course notes for the section 'Comparing3'. If you have not found them already, see the recently updated sticky discussion on 'course hints and tips' here - https://www.duolingo.com/topic/924/hot - for how to get to the course notes