Sylvie doesn't really care about the DA thing (since she doesn't know about it), but she thought Umbridge becoming Headmistress was the shittiest thing ever and might cramp on her making out with boys. Or maybe not as she's be busier.
Her inner Ravenclaw is aghast at the twins not taking NEWTs but she is having the time of her life making Umbridge's life hell at the moment. You can guarantee that she is one of the most troublesome of the students that Filch and his whip are trying to chase around and not catching and in which case, if anyone wants to plot mischief or her going after your character hit me up!