Yes it is haraam but as individuals neither can i or you say anything apart from advise her nothing more than that. If she does not realise the importance of it, I don't see her being a muslim sorry to say. Because if you cannot take part in what your religion is asking to do, and you are just picking and choosing when you want to wear a hijab it is quite pointless. Although it is good that she wears it when she prays or when she is reading the Quraan (holy book).
Loughborough at number 1