You're not horrible. You're not a terrible friend. You have needs and your own issues. Sometimes it gets difficult to listen to other people's troubles if that's what they do a lot of and they seem to use you as their primary soundboard.

Nothing wrong with voicing how you feel. It doesn't have to be mean, accusatory or insensitive. Just state the facts without making what she's doing, as wrong or anything but something you can't handle hearing about all the time. Just be objective in your telling her this. If you are talking about your feellings and needs, it should not hurt her. If she's still upset about it even as you try to be speaking sensitively, that's not really on you.

Think of it this way. If you don't voice how it makes you feel, how it bothers you, how can she be expected to behave in a manner that you want?