Ms. Lovato should know, if she did any research, that numerous NFL players, including the kneeling players, do many of the things she lists.
Her letter was condescending. 
When popular figures called out President Obama, I doubt she insisted those figures cleaned their own house first.
When Republican congresspeople engage in public uber-patriotic displays, does she chide them for being imperfect? I bet not.
Conformity is not a requirement to be a good citizen. 
Kneeling is not disrespectful.