Backbiting About a Non-Muslim and Complaining to Seek Advice
Question

I am a Muslimah for 2yrs. Alhamdulillah, however, my family has not always been supportive of me and at one point my mother wanted to take my daughter and put me in a mental hospital, due to my change. Alhamdulillah, now she is understanding. I was speaking to one sister and I was telling her about my mother and how she treated me; now I am thinking about what happened and it might make her look bad in the sight of that sister. She (my mother) is not Muslim, so does this mean I have committed gheebah (backbiting)! I feel very bad for that because I know she just did not understand due to the American media. May Allah forgive me!!!! Ameen.
Praise be to Allah.We praise Allah for having guided you to Islam, and we ask Him to guide your family and to bring you together on the basis of good in this world and in the Hereafter. The bad treatment that a Muslim encounters from people after choosing the path of Islam is something natural. The prophets themselves were faced with this, and they had aspersions cast upon their honour and their mental faculties. Allah says (interpretation of the meaning): 
“Likewise, no Messenger came to those before them but they said: ‘A sorcerer or a madman!’”
[51:52] 
Gheebah (backbiting) means to say about others things that they dislike. It is permissible in some situations, such as the advice of one who is able to advise you, and complaining about one who is mistreating you. Allah says (interpretation of the meaning): 
“Allah does not like that the evil should be uttered in public except by him who has been wronged” [4:148] 
Mujahid said concerning the meaning of this verse: It refers to the one who has been wronged speaking about the wrong action of the one who wronged him. Al-Adaab al-Shar’iyyah by Ibn Muflih. 
It seems that when you spoke about how your mother has treated you, you did that only for the purpose of seeking advice from your friend, not to tell everybody how bad she is. There is nothing wrong with this, and it is one of the kinds of gheebah (speaking of a person in his or her absence) that are permitted, especially when you have been mistreated.  
The evidence for what has been stated above is as follows: 
‘Aishah narrated that Hind – the wife of Abu Sufyan – said to the Prophet (peace and blessings of Allah be upon him), “Abu Sufyan is a stingy man, and he does not give me what is enough for me and my child unless I take something from him when he does not realize it.” He said, “Take whatever is sufficient for you and your child on a reasonable basis.” [al-Bukhaari, Muslim. 
Abu Hurayrah said: A man came to the Prophet (peace and blessings of Allah be upon him) complaining about his neighbour. He said, “Go and bear it with patience.” He came back two or three times, then he [the Prophet (peace and blessings of Allah be upon him)] said: “Go and put your belongings out on the street.” So he put his belongings out on the street and the people started asking him about that, and he told them the reason. So the people started cursing [that neighbour] and praying against him. Then his neighbour came to him and said, “Go back, and you will never see me doing anything you dislike.”  [Abu Dawood]. 
So there is no sin on you for what you have said about your mother and do not worry about the influence of the American media on her or anyone else, because if you treat her well and give a good impression of Islam, that will bring better results. 
For more information on gheebah and the rulings on it, please see the answers to questions no. 7660 and  23328. 
And Allah knows best.