The difference between different ideological groups and the fiqhi madhhabs – and can she marry an innovator?
Question

                What is the difference between Ahli Sunnah Wal Jammah & other mazhab[ shafeei, Maliki, etc? and can a girl from Ahli Sunnah Wal Jammah marry a man without mazhab?.
Praise be to Allah.Ahl al-Sunnah wa’l-Jamaa’ah are not to be regarded as opposition to the Maalikis, Shaafa’is, Hanbalis and the like, rather they are opposed to the followers of innovated and misguided beliefs and ways such as the Ash’aris, Mu’tazilis, Murji’is, Sufis and so on. The Hanafis, Maalikis, Shaafa’is and Hanbalis are schools of fiqh, whose imams are among Ahl al-Sunnah wa’l-Jamaa’ah, and indeed are among the leaders of Ahl al-Sunnah wa’l-Jamaa’ah. But unfortunately the followers of most of those madhhabs and schools of fiqh have begun to follow the people of innovation and misguidance in their beliefs, so many of the Shaafa’is and Maalikis have become Ash’aris, and many of the Hanafis have become Maatireedis. But with regard to ‘aqeedah, the Hanbalis – apart from a very few – have been spared the change to something other than the ‘aqeedah of Ahl al-Sunnah wa’l-Jamaa’ah. 
The basic principle concerning the Muslim is that he adheres to the Qur’aan and Sunnah according to the understanding of the companions of the Prophet (peace and blessings of Allaah be upon him) and those who followed them in guidance. As for following one of these four madhhabs or any other, that is not obligatory or recommended, and the Muslim does not have to adhere to any one of them in particular. Rather the one who adheres to a particular madhhab in every issue is being a partisan who is guilty of blind following. End quote. 
Hal al-Muslim mulzim bi Ittibaa’ Madhhab mu’ayyin min al-Madhhab al-Arba’ah? By al-Ma’soomi, p. 38. 
There is nothing wrong with following the four schools of fiqh if a Muslim does not have sufficient knowledge to enable him to derive rulings from the Qur’aan and Sunnah himself, but if it becomes clear to him that the correct view is other than that of his madhhab, then he must follow the correct view and not his madhhab. 
Shaykh al-Islam Ibn Taymiyah (may Allaah have mercy on him) said: 
In the Qur’aan, Allaah condemns the one who turns away from following the Messengers and follows instead the religion invented by his forefathers. This is imitation (taqleed) which is forbidden by Allaah and His Messenger, i.e., following someone other than the Messenger in matters that go against the Messenger. This is haraam for everyone according to the consensus of the Muslims, for there is no obedience to any created being if it involves disobedience towards the Creator. Obedience to the Messenger is obligatory for every one, elite and common folk alike, at all times and in all places, both inwardly and outwardly, and in all situations… Allaah has enjoined obedience to the Messenger upon all people, in approximately forty places in the Qur’aan. 
It is permissible for one who is unable to derive rulings to follow a scholar, according to the majority of scholars… the kind of imitation or following that is forbidden by the texts and according to scholarly consensus is that which goes against the words of Allaah and His Messenger. end quote. 
Majmoo’ al-Fataawa, 19/260-266 
The followers of the salaf are those who adhere to the Qur’aan and Sunnah in their beliefs, fiqh and conduct and do not go against what is proven in the Qur’aan and Sunnah and what is agreed upon by the salaf of this ummah. 
Shaykh Saalih al-Fawzaan (may Allaah preserve him) said: 
What is meant by the salafi madhhab is the way of the salaf (early generations) of this ummah, namely the Sahaabah, Taabi’een and prominent imams with regard to issues of ‘aqeedah, sound method, sincere faith and adherence to the beliefs, laws, etiquette and conduct of Islam, unlike the innovators, deviants and those who are confused. 
Among the most prominent of those who advocated the madhhab or way of the salaf were the four imams, Shaykh al-Islam Ibn Taymiyah and his students, Shaykh Muhammad ibn ‘Abd al-Wahhaab and his students, and other reformers and renewers; there is no era when there was not someone who is establishing evidence for the right way. 
There is nothing wrong with calling them Ahl al-Sunnah wa’l-Jamaa’ah, so as to differentiate between them and the followers of deviant groups. This is not praising oneself, rather it is distinguishing between the people of truth and the people of falsehood.  End quote. 
Al-Muntaqa min Fataawa al-Shaykh al-Fawzaan, 1/question no. 206. 
Based on this, if a man whose religious commitment and character are good proposes marriage to a Muslim woman, then she should accept him even if he does not belong to one of these madhhabs, but if the one who proposes to her is a member of one of the misguided and deviant groups, then she should not accept him.  
And Allaah knows best.