Are there any differences in the way men and women are supposed to offer their prayers? At the time of niyyah, can women place their hands like men do (that is below the chest)?

There is no difference between the prayer of men and women as far as the original sources of Islam, the Qur’ān and Sunnah, are concerned. However, biological differences between men and women may demand some distinction. It is also a requirement of modesty that the scholars of later times suggested some practical differences. Adhering to their suggestions is nothing but optional and depends upon one’s own taste and inclination. If a woman considers that the form and style suggested by them seems more close to her nature and that of the requirements of modesty, then she can of course follow their way.

So, women may place their hands on their navel like men or place them on their chest.