If your attempts to get her off the dreary stuff keep failing, then I guess you have to avoid having her around you or let the friendship fizzle out. I think those are your three options. (The fourth would be to let things go on as they are.)

Your time and attention belong to you. The older I get the less willing I am to let people tie up my time and attention in ways that I don't find worthwhile. I used to be a real sucker for anyone looking to glom on and use me to get their attention fix. Now I value my time and attention too much to let people just take it and waste it.

These conversations, or monologues that you hear from her, bring you down and change the tenor of your day. You don't owe that to her, or to anyone. Not on a routine basis. You wouldn't tolerate someone just sticking their hand in your purse and pulling money out of it. Your time and attention are every bit as precious, if not more so. I can think of some dreary company I've kept in the past. I would rather have paid the person $5.00 to leave me alone.

You've heard the expression: it takes two to tango. Well, a boring, dreary person can't really bend your ear, if you just won't listen. At some point, you might have to get a bit ruthless. I know you don't want to be cruel. But she's not as innocent as you might think. I've learned that, when people are basically using you, they know it . . . more than you might think. Start walking away and watch how fast they change the conversation to asking about you. Suddenly they care. It's a case of they say what they think will keep you attentive to them. It's often a game. Don't enable it. You have more power than you give yourself credit for. When you think you've tried everything and nothing works, usually you haven't tried everything.