Originally Posted by Velorien
I would offer a different perspective. Don't try to replace the negative with the positive, because then you're just starting an inner war and hoping the right side wins. Instead, practice listening to the negative thoughts without arguing with them or agreeing with them, without resisting them. "It's OK for you to say that because it's your own opinion" is a good start - it means that you're disidentifying from the negative voice and remembering that you are not it. Once you can do that consistently, the voice ceases to have any power over you - it's just words, it's just a stream of data and energy, like birdsong outside the window.
When you can consistently accept the negative voice without judgement, it will weaken, because it needs you to feed it by feeling bad about it. The more it weakens, the less power it has to influence you. And the more it weakens, the more space is left for all those positive thoughts to arise out of the depths of your being unopposed.
Are you trying to start a war between starting a war between negative and positive and "just listening to the negative thoughts, without resisting them"?
I have done a lot of meditation of the sort you speak, and while it helped me phenomenally with getting past depression and anger, it didn't help me anywhere near enough with anxiety and thinking I was too stupid and not good enough. I can attest that doing as Lioness described absolutely works for the sort of problem that Cheese is having. Maybe what you suggest will be more helpful for her than it was for me, and what I suggest less useful for her, but by no means do I think you're in a position to determine for her what the case will be between the two possibilities. My experience is a huge testament to my opinion on this matter.
I also realized that making positive affirmations is in itself a kind of meditation. It's actually a kind of mantra, and that's something I never did when I was in the monastery or whatever, trying to follow a strict meditative formula... I didn't like it. But I like affirmations; they're my mantras.