Poor you, I feel for you. Unfortunately it seems her standards are not yours, and that must be hard to see. Don't beat yourself up about this, you did what you thought was right at the time and that is all any of us can do.
This is my second marriage and I had a lovely but a slob of a DiL, and I mean a slob. She was fine at first and welcomed me with open arms, but it went down hill from there. Her house got so bad that I refused to go in, which upset her father, but I could not bare to see the sea of clothes on kitchen floor, there was not a clean dish in the house, the dirty plates were left as such, everywhere. The cats use to climb all over them and lick the plates/bowls/pans. The toilet was so dirty I couldn't bring myself to use it.
The whole family tried to do stuff for her, but in the end it was no use, she couldn't or wouldn't see what was wrong. She had 3 children, the youngest at the time was just months old. She laid on her back on the sofa with the baby on her chest and just let the other 2 fend for themselves, until the school got involved and alerted social services and she was only given 4 weeks to pull herself around. She did, but within 5 years she was dead, took her own life.
I am satisfied that everything that could be done was, her father still feels quilty after 4 years, but our children will go their own way no matter what we want, try and make your peace, she will not change for you, just keep an eye on the children and do what you can for them, while you can.
Good Luck and chin up.