She changed her sex to male then she became Muslim

Firstly: 

We praise Allah, may He be exalted, for having guided you to Islam. This is the greatest blessing that Allah can bestow upon a person, because through it one can attain true happiness and eternal bliss and everlasting delight in eternal Paradise. 

We give you the glad tidings that Allah accepts repentance because, by His mercy, Allah makes Islam erase whatever sins came before it, no matter how great, serious and abhorrent they were. At the very moment when you uttered the Shahaadatayn and entered Islam, Allah forgave all your previous sins, including the sex change that you underwent. 

You have turned over a new leaf and started a clean, fresh page with Allah, on which there are no sins, so keep it clean and do not spoil it with sins. 

Ignore the whispers of the Shaytaan (Satan) that he is trying to put in your mind, because he wants to make you despair of the mercy of Allah and think that you are doomed to Hell. But by becoming Muslim, you have been forgiven all your previous sins. 

Secondly: 

Allah created you female, and you have to accept what Allah decreed for you and chose for you. It is not the issue of whether a person is a man or woman; rather it is the issue of whether he or she will be obedient to Allah and attain the pleasure of Allah, whether the person is male or female. 

So you have to go back to the way you were before. 

We asked a doctor and he told us that it is easy, in sha Allah. You can go back to the specialists in this field and do what they advise. 

If the uterus has been surgically removed, that cannot be fixed, but there is no sin on you for that because Islam – as stated above – erases whatever came before it of sins. The same is also true of repentance: it erases sins. You have become Muslim and you have repented and regretted what you did; these are two things, each of which on its own is sufficient to erase previous sins. 

Thirdly: 

With regard to your mixing with men and attending prayers in congregation and Jumu‘ah prayer with them, that is not permissible because you are not a man. You have to conduct yourself on the basis that you are female and follow the rulings that Allah has prescribed for females. 

With regard to mixing with women, there is nothing wrong with that because you are in fact female. 

But if this mixing is going to cause you considerable embarrassment and women will not understand your situation because your outward appearance is masculine, then you can delay that until you change your outward appearance to feminine. You have to hasten to go to the doctor and start to correct the previous mistakes. Until that is done – and we hope that it will be soon – you can focus on learning about Islam through books and articles, and listening to lectures. 

We ask Allah, may He be exalted, to guide you to the truth and make you steadfast in adhering to it; may He open your heart and complete His blessings upon you and grant you peace of mind and happiness in this world and in the Hereafter. 

For more information please see the answer to question no. 146881. 

And Allah knows best.