I can kinda draw some parallels to my mom- (she's gotten better- as an adult I even have a healthy if limited relationship with her after hating her guts for a long time- mind you, she never tossed a kid off a cliff or did some of the other fucked shit). In that sense, I can kinda get where it's coming from- that, and I've been in a perhaps similar headspace of "I want to get out of here no matter what" (not in some marriage or relationship, more of- family and also bad experiences in the country where I was born) if for vastly different reasons myself.
She's manipulative, abusive, and so on. But it's also a kind of hell to be stuck with "family," or a "partner," or environment that makes you feel like less than dirt. Neither of my parents could become better people or even decent without divorcing and my siblings and I were then- and now- glad for it- in my experience of (somewhat similar) feelings- I could try to be happy, but ultimately would come short other than moments of peace and considered- many things, though ultimately my moral compass brought me towards suicidality instead when things happened.
I can empathize with the mom in that sense- my mom had, coincidentally- when I was 2~, held my sister and I over the side of the balcony and threatened to jump. Shit's fucked, but sometimes it's best to just cut out all of the rotten, poisonous convention and peer pressure and say "fuck it" and leave. Rather than torture yourself, or mentally fuck up your kid, brain damage another and so on.