The house of Lady Fatima AS was being attacked by a group of Saqeefah people to force her and her husband and her family to give allegiance to the Saqeefah government. that was the reason of the very early demise of Lady Fatima AS. We believe that That attack was the reason for her martyrdom.
The attack on the house of Fatima Zahra (AS) has been admitted by leading Sunni leaders including Abu Bakr himself who openly said when he was about to die that I wish that I did not attack the house of Fatima even if it was a center of war against me. This is narrated by eminent Sunni scholars like:
1. Al-Tabarani in al-Mo'jam al-Kabeer ,
2. al-Dhahabi in Meesan al-E'tidaal,
3. Ibn Qutaiba and quoted by Ibn A'bd Rabbih in his book al-E'qd al-Fareed.
4. al-Mas'oodi in amorous al-Dhahab.
5. Ibn Asaakir in Tareekh Dimishq.
6. al-Haithami in Majma' al-Zawaa'id.
7. al-Soyouti in Musnad Fatimah
8. al-Muttaqi al-Hindi in Kanz al-Ummaal.
Beside this, we have hundreds of Sunni books who narrated about the attack and fire to burn the house or door of Fatimah e.g.
1. Tareekh al-Tabari , V.2, P. 443.
2. Mussannaf Abi Shaibah, V. 8, P. 572.
3. al-E'qd al-Fareed , V.2, P. 73.
4. Ibn Abd al-Barr in al-Estee'aab, V. 1, P. 298.
5. al-Waafi bil Wafayaat by al-Safari, V.2, P.227.
6. Kanzul Ummah , V.5, P.651.
7. Abul-Fidaa' in al-Mukhtasar Fi aakhbaar al- Bashar, V.1, P.107.
8. Ibn Taymiyyah (the staunch enemy of Ahlul Bayt) in his book Minhajul Sunnah, V.8, P. 291.
9.Ibn Hajar al-A'sqalani in Lisaan al-Mizan, V.1, P.111.
10. al-Dhahbi in Milan al-E'tidaal, V.1, P. 139 and in Siyar A'laam al-Nubalaa', V. 15, P. 578.
11. Al-Tabarani in al-Mo'jam al-Kabeer , V.1, P. 17.
12, Al-Haithami on Mo'jam al-Zawaa'id, V.2, P. 353.
and many other Sunni sources.
Wassalam.