The question is already mentioned in the topic, Shias claim that Fatima (r.a) is superior to eleven Imams. What is the basis of this superiority? Because we know that she was neither a prophet nor an imam. So how is she superior to eleven imams if imamate is considered a higher rank than the prophethood by Shias.
The position of Fatima, Sarah, the two Mariams (peace be upon them all), is explained in Quran. Women are in need of inspiration and Mariam (s) is also one of the Imams who guide by God's command per Suratal Anbiya and part of the course that is one course for humanity, the course of God's chosen ones.
Spiritually Fatima (s) can appear and connect people in the unseen to God just like rest of Imams (a) can and Imam Mahdi (a) can connect us to any of the Ahlulbayt (a) who can spiritually help us and they are the stars of the sky of this world. Fatima has the star brightness role and she is among those weapons against Iblis and his forces and among the lights that are a refuge and sanctuary from Satanic forces.
The difference is she will not lead militarily - that is the only task that is not for women that she is not of the Captains that navigate society but rather she did call politically towards Ali (a) but she won't be leading militarily if an uprising would have occurred.
That said, Ahlulbayt (a) are all equal rank.
As for the first Mariam (a), the sister of Musa (a) and Harun (a), you know when you read about Mana in Quran, that was through her hands, God fed bani-Israel through her hands. And the curse of Bani-Israel when they started to make a ugly lie about that Mariam (a) and Harun (a) and ended with their words of killing the anointed king from the line of David (a) who is not dead but to return.