Why pity?

"CARIOLA: Whether the spirit of greatness or of woman
Reign most in her, I know not, but it shows
A fearful madness. I owe her much of pity."
(I.i.505-507)

There were a few lines in this act that I found to be either really interesting or amusing, but these three lines spoken by Cariola were the ones I found to be most intriguing. I wonder what she means by "fearful madness" in this. Does she mean that the Duchess's actions mimic madness, or is she referring to the madness of her brothers not wanting her to re-marry, and that the only reason that she married Antonio was because she feared that madness and wanted to escape it? (did that even make sense?) Also, she just served as the witness of the Duchess's marriage to Antonio. Why does she feel that she needs to pity the Duchess? Is it because she realizes that she married Antonio out of desperation? Is the Duchess truly mad? Or does she know something about Antonio that we do not know yet?

I find it strange that the Duchess chose to marry Antonio so rapidly. Aside from Antonio's praises, there was not much sign of the two being romantically involved before that -- unless I completely missed it. So I wonder if she did this as a way to rebel against her brothers, or if she is truly in love with Antonio. Obviously she wanted to re-marry, but I also wonder if she intended to do this when she called for Antonio, or if she did not think of marrying in secret until her brothers brought it up (I.i.321-328) and decided to do it to spite them. Whichever the case, I really think that the Duchess is a pretty conflicted character, but at the same time, she is also standing up for herself and doing what she wants even if it goes against what the males want her to do. A bit of feminist strength for sure... at least for now.