The Prophet salla Allahu alaihi wa sallam has told us that whoever doesn’t pray at all is not a Muslim. Therefre, it appears that your sister is not a Muslim anymore and that you should start with her from scratch. You should reason with her and talk to her in logic as she doesn’t believe in the Quran or in Islam.

Try to talk her into confessing of the existence of Allah, the Creator of this universe and of His beautiful names and attributes such as the Wise, the all knowledgeable and the Strong.

Once she acknowledges this fact, then you can go on to say that it can’t be that such a supreme being creating such perfect creation and not tell His creatures what He wants from them. it is like Sony making a sophisticated electronic device without printing a user’s manual.

Then talk about the Messengers of Allah concluding with our Prophet and the Quran.

This might help.

I have a sister that doesn’t pray.We always ask her to pray but she says that there is no point of praying because i don’t do anything bad and i’m always clean. There is no reason for me of praying.She also doesn’t fast and we always try to help her but she doesn’t do it. we told her the five pillars of islam and we give her the quran to read but she says i don’t know how to read and i don’t know the reason why i’m reading it. can you give us some advice to help her understand and make her a proper muslim.