VBerhan:

Thank you so much for this explainer!

This makes me wonder, though: why would she intentionally want to become a concubine?

Yes, she's an orphan from a military household not of equal status. But why would she forego the right to become someone's 'proper' wife, even if that someone was of slightly lower status than the ML?

From my understanding, unless you married the emperor, being a concubine — even at the highest levels, e.g. to a wang/fief lord — still kind of sucked, right? (at least that's what I took away from my watch of "Are You The One" and "Blossoms In Adversity" and the ensuing googling-spree, because I first didn't get what being a concubine or a second wife entailed — including, apparently, forfeiting the right to raise your own kids!)

Miss Du is 19 and her marriage was delayed for a long time because she originally wanted to be a female official (something that Eldest Madam Lin revealed when she was talking to Second Madam Lin), I don't think she wants to be a concubine but considered her options based on her current age and predicament.

Lin Jinqi is from a noble family and was recently divorced amicably, he's probably the best option and even if she was a concubine first, she's capable enough to scheme her way to become a legitimate wife after she has a child (after all the Lin family has very few male heirs - even Zhao Xingtang was pressured to have children)