1)
Why did she mention that the other gave birth three days later?
1.
Kli Yakar citing Mahari: She thought that perhaps Shlomo can distinguish a baby born before three days from one born after three days. 1
2)
Why did she repeat "we were together"?
1.
Malbim: We were not in separate rooms, rather, in the same room.
3)
Why did she say both "Ein Zar Itanu ba'Bayis" and "Zulasi Shetayim Anachnu"?
1.
Malbim: No one else lived in the house, even in other rooms.