Ruth probably choose to ignore hints that were pointing at how Finch was treating her daughter and granddaughter. She lacked the strength, courage, and sense of responsibility to protect these girls. On some level, she is probably also a victim (not in the same sense as Sarah and her mother though), but I do not feel sympathetic towards her. She is a grown-up person and capable of taking care of herself and her child and grandchild. She choose to abandon her responsibilities because that was easier.
I had no inclination to feel sorry for Ruth. You need to be aware of what is happening in your own home. Eyes wide open I believe that some individuals choose to stay in unhappy marriages because of stability or for other reasons.