I think there are a few aspects to this, and it’s easy to jump to judgement because relationships are such emotionally loaded topics.
My personal instinct would be not to judge but to feel sorry for her. I’ve been in a long marriage myself (to what most would call a good man) and I left because I no longer loved him. Some people might see that as selfish, because it affected my DC, but had I stayed, others would have judged me for living a lie. People will judge either way. My lifestyle suffered as a result of my choice but that was my choice and I am glad I made it.
But we’re all wired differently. For some, love and emotional connection are non-negotiable; for others, companionship, family stability, or shared lifestyle matter more. Historically, many marriages functioned as partnerships of duty or practicality rather than romance - and for some, that still works.
My advice is to try to step back from judging and instead recognise the complexity: staying isn’t always cowardice, and leaving isn’t always bravery. Both come with their own kind of pain.
If I were in your shoes, I’d probably just keep an open ear for your friend if you can - she clearly needed to offload. Suggesting couples therapy sounds entirely reasonable, as long as it’s offered gently, without pushing. Sometimes people just need to be heard before they can even work out what they feel.