aw i love the whole family, except for estelle's original mother. she doesn't count
I think way too much about how we've managed to completely switch around the original meaning of "blood is thicker than water" somehow over the years. The original full version is "the blood of the covenant is thicker than the water of the womb," which is to say stuff like bonds forged between comrades are stronger than those caused by something nobody can control like who your relatives are. I'd say the only reason "blood is thicker than water" ever works at all is because some people manage to forge decent bonds more along the lines of comradery within their families. Often, you see people further corrupting the original meaning of it by just using this arbitrary bond to take advantage of the kindness of someone related to them. Honestly, this is probably how the phrase evolved into the modern usage. A quick little edit and suddenly you can guilt some poor sod into helping you.
In this story, you can see how the mother probably didn't put much stock in either of the intended versions of the saying, for instance. She's my daughter? So what. We've lived together for years and should have probably bonded over that time? Nope. She's totally one of the ones attempting to use an arbitrary bond for personal gain. Her blood relation to the daughter she doesn't seem care about gives her an in with the duke who should most likely be the child's father, so she went after his money.