I'm not making judgements, and I'm not medically trained.
People should feed how they want to, and I would absolutely never question how anyone feeds their baby, their child, or themselves. I just have a much easier time with people who say "I am too lazy to cook, so I buy ready meals", than people who say " I can't afford to cook from scratch".
I tell my music students to say "I didn't practise this week because I didn't want to (or I had other things I preferred to do)", rather than "I was too busy to practise."
I do loads of things which aren't great just because I choose to do them. I try to admit this to myself and to other people when appropriate.
If your friend said: "I know it's probably healthier for my child to breastfeed, but I couldn't deal with having all that responsibility, and I didn't like the feeling of it." I would think that was completely fine, and wouldn't dream of judging.
I also think it would be completely fine for your friend not to talk about her feeding choices.
I'm prepared to admit I might be wrong about most people being able to breastfeed, but I would like to see some research about what percentage of healthy, well-nourished mothers in societies with no access to formula are unable to feed their babies. I'm sure there would be some, but I imagine it would be a small percentage.