I 1000% agree with you that it was the mothers responsibility that she should have put in more effort in being a family but I think this is what happened.
*I would like to say first though, this is pure speculation and conjuncture on my point so take what I'm about to say with mountains and mountains worth of salt
*
I look at the mother character as what happens when you strive to be the best and forget about how to live like a ordinary human being. Let me explain with comparing her to the sisters before they met Yuu. Their lives are heavily regulated. Everything is measured by efficiency over all else. Intense work was not only expected, but the bare minimum to be the best. The absolute top is within reach, as long as you put in the time and effort required. Prayer? Luck? Crutches! Taste? Does that affect the number of nutrients? No? Not needed. I might be dramatizing a little, but I don't think by that much haha. In fact, that's probably why they're so bad at regular housekeeping. Why focus on anything that doesn't directly affect their goals?
Things like family? In their eyes, I'm including the mother/sisters/their father in this, it's only natural that they drift apart. Regrettable for sure, but it's the price that you pay sometimes. Yuu has a small conversation with his mom after years of not really talking with one another. The sisters sit down with each other to have a meal for the first time in so long. The father is confronted by his three daughters together(Chapter 55). You notice how shocked they are. But they're ultimately happy about it. They do love each other, but forgot how to be a family.
I think what happened with the mother specifically was that she just didn't know how to fix the relationship once it ultimately fractured then it was too late. Given what I wrote earlier, was there any real shot on working things out? She probably felt like it was her fault ultimately and didn't know how to bridge the gap. She seemed to me awkward when it comes to her son. Like, she's close but misses at the end sometimes ie: chapter 46 pg 5 - 8 and chapter 66 pg 19. She might even had hopes in repairing the bridge in the future. But impending death kinda ruin that shot. Might even put things in perspective. Sure, she would miss acting, but ultimately what she missed most was the opportunity to have a family, like the one she acted in.
Ultimately, I don't absolve her of responsibility or put the fault on Yuu on how they ended up. I just see the context on how it happened. Or really, put a lot of conjecture on my part lol.