I agree with @Dangosan. Check the .ust, make sure you don't make her sing romaji lyrics first.
And i think this thread is misplaced, @kimchi-tan can you please move this thread to its section? Thanks in advance^^
Uta requires .ust that's CV and hiragana (notes should be as such 「あ」「り」「が」「と」). The default resampler or fresamp is preferential in rendering and you should also do some work on the oto to eliminate some of the choppiness. Make sure the .ust has been fitted to the voice and any red exclamations eliminated.