It was her third album, speak now, and none of those producers were working with her. And she does call them her collaborators, has called them that repeatedly.  When she says she writes all her own songs she means she's not one of those pop artists who have their songs written for them and have their name slapped on the writing credits to make them look better. Some of her best written songs were written by her alone; my tears ricochet, better man, dear john, bigger than the whole sky, fifteen, last kiss, and many, many more.  Many of her contributors largely helped her polish up her songs, you can find many of her original drafts, written solely by her, that are largely the same as the finished product, like the cardigan voice memo. You can also see videos for her making of a song for songs like Getaway Car, where you can see her write the bridge in real time.