All praise be to Allah.
Many women face the surge in jealousy because of polygyny. It is natural in women as we know of the jealousy of ‘Aa’ishah (may Allaah be pleased with her) concerning the Messenger of Allaah (peace and blessings of Allaah be upon him).
A woman’s jealousy concerning her husband is innate and natural. One cannot simply tell a woman “do not feel jealous because of this.” If a person dislikes something even though it is prescribed in sharee’ah, that does not adversely affect him, so long as he does not hate the fact that it is prescribed. Allaah says (interpretation of the meaning):
“Jihaad (holy fighting in Allaah’s Cause) is ordained for you (Muslims) though you dislike it, and it may be that you dislike a thing which is good for you and that you like a thing which is bad for you…” [al-Baqarah 2:216]
If a woman feels jealous but does not hate the fact that Allah has allowed a man to marry more than one woman, but she hates to have a co-wife then there is not a sin on her because there is an obvious difference in both of these. Allah does not punish us for what we feel. A feeling is natural and arises based on some situations and circumstances. It is, however, our actions that define us. If a woman who is jealous hates the shariah or try to harm the co-wife because of jealousy then that is obviously a grave sin and liable to the wrath of Allah.
A woman must also try to find sabr in prayer and doing good deeds and InshaAllah Allah will make her strong and make her bond with her husband stronger so that she may not feel inferior or jealous. A muslimah must strive to live peacefully with her family.
And Allah knows best.