If someone were to ever call me clingy, I'd immediately stop talking to them and go on a friend diet with that person for a week or two. If they text me I'd be really slow to respond.
It's not your job to analyze your friend’s relationship. If she wants your advice she'll ask you for it. Don't offer it up if she hasn't asked. Yeah it sucks watching people suffer through ugly relationships. But there's nothing you can do about it other than be a good friend, and if she's calling you clingy, then you aren't doing that. Lay off for a bit and take a chill pill. You're probably taking this way more seriously than you need to be.