What is the ruling on doubting the existence of God and contemplating His essence, which happened to a committed girl studying philosophy, and is this considered a doubt in faith, or apostasy and hypocrisy?

It is not permissible to study philosophy except for one who is firmly grounded in the Islamic sciences or is knowledgeable in Islamic law, in order to clarify the truth and the falsehoods of philosophy. The doubts that afflict hearts are from Satan. The questioner's fear of disbelief (kufr) or hypocrisy (nifaq) is a good sign, and these thoughts should be repelled by saying: "I believe in Allah," and seeking refuge from Satan, as this is a clear sign of faith. Contemplating the essence of Allah is from Satan, and it should be repelled by contemplating His creation, for whatever comes to mind, Allah is greater than it. The questioner should refer to people of knowledge, and accuse the intellect of deficiency, not the Sacred Law, and accompany righteous women, and frequently supplicate: "O Turner of hearts, make our hearts firm upon Your religion."