Your comment kinda confuses me, because the OGFL doesn’t get sold off, she chooses the older man so she won’t be poor anymore. The problem was that she saw herself as everyone’s “angel” and thought she deserved to be worshipped and praised. When the prince comes along she gets excited because she believes she deserves to be something as important as the empress and does everything she can to manipulate the prince into marrying her. I’ve also read the novel which definitely has additional context but OGFL biggest downfall is her own narcissism. OG Ophelia’s actions weren’t right, but we see that she retaliated the amount she did because of OGFL straight up lying about Ophelia’s actions especially since originally her family was close to the prince and OGFL didn’t want her to even be friends with him anymore due to her own jealousy. Having read the novel it makes more sense later down the line how terrible she really is unfortunately

Tbh I really hope the heroine ends up divorcing her husband and leaves the crown prince. Like poor girl has been through enough having to deal with being sold off to that nasty old man to survive and then find out the woman who was vile to her is now getting close to the man she loves.
Like I'm not a fan of female characters acting as a victim to secure pitty to get the upper hand, and I do feel bad for the female lead for what the heroine does in retaliation. But the situation is bad for both of them. Like they both are trying to survive and both are flawed, so why not team up??
Edit//
I feel like the heroine at first had a very interesting set up to be a more dynamic character. She's been through a lot, losing her social status, having to sell herself off. And then she found someone who drew out her empathy and then turned into a person who could one help her out of her situation and two kinda gave her the attention and affection she craved. Like you have so much to work with. First off she comes from a family of merchants so why doesnt she have characteristics of a merchant, instead they make her hate materialism, but she also ends up becoming materialistic in an attempt to copy the female lead. Shes someone who will sacrifice herself for her goal but then she resorts to lying about being asulted instead of finding a way to undermind the female lead. Like there is no planning, they're acting like the heroine if doing all this out of desperation but the writers treat her like a petty two faced bitvh instead of a deeply wounded and wary woman who is fighting to survive.