So, your English phrase is a little confusing, and I would recommend you not try to recreate the exact same sentence structure in Japanese. Translation is never very straightforward and direct, especially between English and Japanese.
If you're saying that the book that lady is reading is amazing, I'd probably use a clause to modify the noun "book."
あの女性が読んでいる本がすごいです。
Honestly, I would probably avoid making a statement so direct and definite as "that book is amazing," in favor of something like "I think that book is amazing, すごいと思います" or "it's a favorite of mine,気に入ったのです" or something along those lines.
If you're saying that it's impressive that she is reading that book (perhaps because it's long or complex, or like she's reading something difficult in another language), the structure would change so that instead of the book being the subject of the sentence, you'd nominalize the act of her reading that book: 彼女があの本を読んでいるのがすごいです。This does strike me as a little condescending, but I've had Japanese people tell me something along these lines when they saw me reading a novel in Japanese so I wouldn't say it necessarily carries that nuance to native speakers.