Most first wives only stay with the husband after second marriage because of some majboori, not love.
Frankly speaking, if a man truly loves a woman and sees no weakness in her he would never feel the need to have second marriage. Many men are unable to have kids with their wives but still stick with her through thick and thin instead of being selfish and doing second marriage.
I dont see any positives in second marriage. But after a man has done second marriage, usually first wife stops trusting him and loses all respect for him. I know I would too.
In the end, it should be her own personal choice if she wants to stay or leave. Nobody should pressure on her