By Shaykh ‘Abdul-‘Azeez Ibn ‘Abdullaah Ibn Baaz (d.1420H)
[Q.1] `What do you say about the woman’s role in calling to Allaah?’
[A.1] `She is like the man, she should call to Allaah, and order the good and forbid the evil, since the texts from the Noble Qur`aan and the Pure Sunnah prove this, and the words of the scholars are clear about this. So she should call to Allaah, order the good and forbid evil in accordance with the manners prescribed in the sharee’ah (revelation) which are required from the man. 
Along with this, she should not be diverted from calling to Allaah by impatience and by lack of perseverance due to the fact that some people belittle her or abuse her, or make fun of her. Rather, she should bear that and patiently persevere – even if she sees something from the people that may be counted as being mockery.
She should also take care of another matter, which is that she should be an example of chastity and cover herself with hijaab in front of males who are not mahram for her and she should avoid mixing with men. Rather her da’wah (call) should be done while taking care to avoid everything for which she would be censured.
So, if she gives da’wah to men, then she does so while wearing proper hijaab and without being alone with any one of them. And if she gives da’wah to women, she does so with wisdom and pure manners and conduct so that no one remonstrates with her and asks her why she does not begin with herself.
She should also avoid clothing which, will be a trial (fitnah) for the people, and she should keep far away from every cause of fitnah , such as revealing her beauty and speaking in a sensual manner – which would be censured. Rather, she should take care to call to Allaah in a manner which will not harm her Religion, or her reputation.” 
[Q.2] `What is the knowledge needed by a caller to Allaah and for ordering the good and forbidding evil?’
[A.2] “It is necessary for the (Daa’ee) caller to Allaah and who is ordering the good and forbidding evil to do so with knowledge. Allaah states: “Say: This is my way, I call unto Allaah upon knowledge ( ‘alal-baseerah ).” [Soorah Yoosuf 12:108]
Knowledge is defined as what Allaah has stated in His Noble Book, or what was stated by the Messenger ( sallallaahu ‘alayhi wa sallam ) in his authentic Sunnah . Both actions should be based on the Noble Qur`aan and the Pure Sunnah . The caller will know from them what Allaah has ordered and what He has forbidden. She will know the methodology of the Messenger (sallallaahu ‘alayhi wa sallam) in Da’wah to Allaah and disavowal of evil, and the method of his companions (radiyallaahu ‘anhum).
The caller can do this by looking at the reference books of hadeeth and paying close attention to the Noble Qur`aan and referring to the statements of the scholars in this regard for they have written much on this topic and laid the necessary foundation. What will put one in position to fulfill these matters is to give attention to it to the point that they are upon clear knowledge of the Book of Allaah and the Sunnah of His Messenger (sallallaahu ‘alayhi wa sallam) in order to put matters in their proper place. The caller can put the call to good in its proper place and ordering to the good and forbidding the evil in its proper place clearly and with knowledge until they will not fall into disavowing or forbidding a wrong with what may be worse. Also to not call to good in a manner which may lead to an evil worse than if they merely left off calling to that good thing. The point is to emphasize the necessity of the caller possessing knowledge so that they may put matters in their proper place.” 
[Q.3] `If a believing woman sees someone from her near relatives committing some sins, then what should her stance be?’
[A.3] “She should forbid the evil in a good manner and with good words, gentleness and kindness – since it may be that the sinful person may be ignorant or ill-tempered and if they are strongly censured it will only make them worse. She should therefore forbid the evil with a nice manner and good words and with clear proof from what Allaah and His Messenger said and while making du’aa (supplication) for them that they be guided so that estrangement is not caused between them. This is how ordering the good and forbidding evil should be. It should be with knowledge, insight and clarity, gentleness and forbearance as will help the one being censured to accept it and not be averse and resist it. The one ordering the good and forbidding the evil should therefore endeavor to use words which one hopes will be a reason for acceptance of the truth.” 
 Refer to the following fatwaa (Islaamic ruling) for a clearer explanation of this point.
 Majmoo’ul-Fataawaa wa Maqaalaatul-Mutanawwi`ah (4/240) of Shaykh Ibn Baaz
 Majmoo’ul-Fataawaa wa Maqaalaatul-Mutanawwi`ah (4/232 – 233)
 Majmoo’ul-Fataawaa wa Maqaalaatul-Mutanawwi`ah (4/233)