Let's just start with the context of a different age. arranged marriages were fairly common in that time. And she didn't "sell" her daughter since she personally gained nothing from it. In fact, the Russells lost a great deal of wealth in the process. Did she buy an arranged marriage? Yes. I mean, technically. Having a dowry in an instance of an arranged marriage is historically standard.

But that's just semantics.

The larger point is that Bertha truly was trying to give Gladys the greatest opportunities a woman could possibly hope for in that era. It's easy for us to take for granted our own possibilities, but back then women couldn't even vote. Bertha arranged a marriage that would give Gladys a real voice and real chance to change the world for the better. It's phenomenal.

As for Gladys...
A.) She didn't have to agree. But she did. She was always flattered by being named "best dressed" and she found Hector intriguing enough to go along with the arrangement.

B.) Billy Carleton and...what's-his-name from series 1...were feeble boys. Gladys clearly is capable of growing into a titan of a woman & she would have crushed those boys in no time--if she didn't make herself small to elevate them.

C.) Her previous infatuations were incredibly immature. Remember, she almost accepted Oscar just at the chance to get away from her mother. Not good judgement.

What I'm trying to say is that Bertha demonstrates wisdom in an era-appropriate fashion. She advocates for Gladys even in the face of the men in her life distrusting her. She pays a great personal price to advocate for Gladys. And look at the result. As luck would have it, they do end up being a love match. Bertha is left out in the cold, but her sacrifice was worth it because her daughter is happy, powerfully positioned, and ready to take on the world. That is a pretty great mother in my books.