It is too difficult for her to do ghusl from janaabah so she does not pray, then she repents, then she does that again.
Question

                There is a woman who prays, then stops praying, then wants to repent. She does not pray because she has intercourse with her husband then delays doing ghusl, then she regrets it again. Sometimes she does not pray for a whole week.
 She wants to repent but she feels that will not do any good. She is afraid that she will do that again and that the Lord of the Worlds will never forgive her.
Praise be to Allah.Prayer is the greatest pillar of Islam after the Shahaadatayn, and the one who does not pray out of negligence or laziness is a kaafir who is beyond the pale of Islam, according to the more correct of the two scholarly opinions, because of a great deal of evidence to that effect, such as the words of the Prophet (peace and blessings of Allaah be upon him): “Between a man and shirk and kufr stands his giving up prayer.” Narrated by Muslim, 82. 
And he said: “The covenant that stands between us and them is prayer. Whoever gives it up is a kaafir.” Narrated by al-Tirmidhi, 2621; al-Nasaa’i, 463; Ibn Maajah, 1079. 
How can a Muslim woman willingly expose herself to being classed as a disbeliever in Allaah just because she finds it difficult to do ghusl? In fact it is not difficult to do ghusl, apart from the tricks that the Shaytaan tries to play on people. 
This sister has to fear Allaah and His punishment. She should hasten to repent sincerely before the destroyer of pleasures and separator of people (i.e., death) catches her unawares. She must start praying again and continue to do so, and she should become one of the people of purity and cleanliness, for Allaah loves those who repent and He loves those who are pure.
 Her fear of going back to sin should motivate her to adhere to obedience and persist therein, not to fall short and be negligent. The believer should feel aware of Allaah and realize that Allaah accepts the repentance of those who repent, and guides further those who follow His guidance. Allaah says (interpretation of the meaning): 
“Know they not that Allaah accepts repentance from His slaves and takes the Sadaqaat (alms, charity), and that Allaah Alone is the One Who forgives and accepts repentance, Most Merciful?”
[al-Tawbah 9:104] 
“And Allaah increases in guidance those who walk aright. And the righteous good deeds that last, are better with your Lord, for reward and better for resort”
[Maryam 19:76] 
“As for those who strive hard in Our Cause, We will surely guide them to Our Paths. And verily Allaah is with the Muhsinoon (good doers).”
[al-‘Ankaboot 29:69]
Allaah forgives all sins for those who repent to Him, as He says (interpretation of the meaning): 
“Say: “O ‘Ibaadi (My slaves) who have transgressed against themselves (by committing evil deeds and sins)! Despair not of the Mercy of Allaah, verily, Allaah forgives all sins. Truly, He is Oft-Forgiving, Most Merciful”
[al-Zumar 39:53]
And Allaah knows best.