From that which makes a Muslim happy is his seeing people enter into the true religion of Allah, the Exalted and leaving their false and distorted religions. We'd like to congratulate you on having been chosen by Allah for Islam and then for being granted the ability to call towards the guidance which resulted in the Islam of your sister and her being saved from the wrath and punishment of Allah. This takes our minds back to the glorious companion, Abdullah ibn Salam, who was a Jew and who entered Islam and perfected his Islam. We ask Allah, the Exalted, to keep you and your sister firm and to grant you the strength and ability to attain beneficial knowledge and work righteous deeds.
From that which we advise you to do with your sister who entered Islam in order to help keep her firmly upon the religions is the following:
1. Encourage her to recite and to listen to Quran a great deal. It would be nice if you could assist in selecting recitations of recitors whose voices are pleasing to the listeners.
2. Make available to her small but highly beneficial Islamic books which contain simplified Islamic rulings and the biographies of great Islamic scholars and leaders. It would be preferred if they contained biographies of female scholars, callers and warriors.
3. Make every effort to keep her away from bad company, especially those friends which she had before Islam and who had an impact on her due to their strong personalities or gentleness. Be gentle while doing this so as not to turn her away from you and have her more attached to her friends.
4. Make easily accessible to her touching audio materials which talk about Islamic issues and the fate of man after death and the hereafter.
5. Encourage her to regularly praise and thank Allah, the Exalted, for the blessing of guidance. Through gratitude, blessings last and every slave requires of his Lord, the Exalted, to assist him, strengthen him and keep him firm upon his religion.
6. Encourage her to pray regularly and on time while giving the prayer its due by carrying out its necessary and compulsory actions in the best manner and urge her to supplicate abundantly during the prostration.
7. Be sure to tell her not to reveal her reversion to Islam to her family at this time out of fear that they will influence her negatively and cause her harm in her religion. See the answers to the two questions 33827 and 69752.
8. The fact that you were able to influence her and she accepted Islam after observing you shows that she respects you and has love for you. Therefore, try to be her best friend and the rock she can lean on. Try your best to give her all the moral support you can; continue being a good example for her, let her talk to you and share her thoughts with you and let her feel that you are there for her whenever she needs you. Insha Allah your companionship and support will be a positive influence on her.
9. It goes without saying that perhaps one of the most effective means (if not the most effective) is for you to regularly and consistently supplicate to Allah (du'aa) for her. Everything is in Allah's Hands and He is the One Who controls the hearts, therefore, implore Him to keep your sister firm upon the truth.
10. Gently try to help your sister find a new set of friends who will be supportive and act as good role models.
We ask Allah to keep you both firm upon His religion and to grant you success in pleasing Him. Thank you for taking the time to benefit from our site.
May Allah grant you beneficial knowledge and the ability to act according to it.
Reproduced from Islam QA