As she points out, it's not really that "was" is bad and in some cases it's exactly what you want, but it could be a sign that the writing isn't as fluent and vivid as it could be. Therefore, rather than seeing "was" as intrinsically bad and trying to twist sentences around to avoid it, you should regard it as a warning signal that something isn't quite right. I love her final warning!
"But it seems to me that you can't possibly work out what to do about a sentence which has set the alarm off, if you don't understand what's really going on inside it. It's a bit like realising that the canary in your mine has stopped singing, without knowing why it's dead or what you should then do. Swapping it for a blackbird isn't going to help."
Anyway, it's just as well these "was" haters aren't writing in Welsh because Welsh uses the imperfect/continuous past far more than English does. So where in English you would say, "I lived in London for two years," in Welsh you would say, "I was living in London..." Similarly, "I thought it looked different!" would be "I was thinking that it is looking different!"