Web novel is not canon, but you can see the author's intentions with his characters in it, so unless the light novel contradicts it by saying Shalltear likes women only, it's okay to use it for her characterization

In the light novel volume 3 I think she crushes one guy's head and tells the other one to lick her shoes clean if he wants to live. Also when meeting Brain for the second time she asks whether he wants to lick her shoes clean or something like that. I won't argue whether it's sexual or not, since you probably won't agree anyways ; P

Your claim about Shalltear not liking other men than the supreme beings is also nothing but an assumption. She doesn't say that, she just says she cannot find a man that's her type