It is entirely up to you and her. My wife followed the same path, and she did file the N400 when her filing window opened, and about 6 months later, she had her US passport. In my eyes, the N400 runs on its own timeline, and if naturalization is the ultimate goal, there is no real reason not to file when possible. In some ways it may kick start the ROC process as the I751 is supposed to be transferred to your local office for processing when the N400 has been filed. That usually happens, but there have been stories where it did not.
Anyway, whatever you choose, good luck!