All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, sallallaahu 'alayhi wa sallam, is His slave and Messenger.
Shariah (Islamic law) permits a husband to marry a second wife, provided he maintains justice between his wives regarding observing the night’s turn and providing adequate maintenance. Allah, the Almighty, says: {Then marry those that please you of [other] women, two or three or four. But if you fear that you will not be just, then [marry only] one.} [Quran 4:3]
Any condition stipulated by the second wife that contradicts this principle of fairness is invalid, and fulfilling it is impermissible. You must provide your other wife with her rights if you marry that (second) wife.
If she agrees to marry you while you uphold justice between your wives, then proceed. Otherwise, it is best to reconsider and seek another wife. Marrying a second wife while being unjust to either wife carries severe consequences. The Prophet said: “Whoever has two wives and inclines toward one of them will come on the Day of Resurrection with one of his sides leaning” [Reported by Ahmad, Abu Dawud, Ibn Majah, and others, and graded as Sahih (sound) by Al-Albani].
Allah knows best.