Does a girl have the right to ask to see her suitor if he does not ask to do so himself? And is that considered a lack of modesty? And what should a girl do if her family refuses the Shar’i viewing? And how should a girl behave regarding attending wedding parties that contain forbidden acts?

It is Sunnah for the suitor and the one being sought to look at each other, so they can decide whether to accept or reject. This is not a matter of lacking modesty. A girl has the right to refuse marriage to someone she is not pleased with. However, she should not reject the suitor and disobey her parents merely because the suitor has not seen her, as the suitor's viewing of his fiancée is a Sunnah and not a condition for the validity of the marriage.