Another way to look at this is to consider the phrase, “it doesn’t hurt to ask.” The roomie wanted the tv in the common room, so rather than keeping quiet she asked because it doesn’t hurt to ask. It doesn’t make her a bad person to ask the question. The implication to “it doesn’t hurt to ask” is that you expect to receive either a yes or no. So as the person being asked, just say no. Asking the question only makes her a bad person (in your mind, not in reality) if you’re incapable of saying no.
Seriously, you’re going to need to get used to wearing those big girl pants for the rest of your life because lots of people will be asking you for things where you’ll want/need to say no. Another phrase to consider is, “Just say no.” Embrace it, love it, it will free you from a lifetime of anxiety. Seriously.