。
She held back from publishing her first novel.
Literal
She [topic-は] first [of-の] novel [object-を] publish [nominalizer-の] [object-を] reconsidered.
思いとどまる means to reconsider, hold back, or refrain from doing something you were about to do — it carries the sense of pulling back from the brink of a decision. The の nominalizer packages 出版する (to publish) into a noun clause that serves as the object of 思いとどまった. 初めての小説 = 'first novel' — the の connects 初めて to 小説 as a modifier. An interesting glimpse of creative self-doubt.