I second this, I personally never got into Blyton and found them quite dated. What gets me though is that she has given a book 2 stars, but doesn’t seem to have given any written review? I’d love to see why she gave it what she did!
Her ratings often have no bearing on the vague reviews she gives for the books, like she changes her mind as to what fake opinion she'll have and forgets to keep it consistent.
Back when she actually left reviews, in amongst the vague, word soup reviews for books she clearly hadn't read, there was nonsense like:
"This is the greatest work of literature ever written! 4/5 Stars."
"I enjoyed parts of this, but overall it was very disappointing. 5/5 Stars."
"This book was amazing! I cried several times and highly recommend this to anyone! 2/5 Stars."
My gut answer for her dislike of Famous Five would've been that they're quite dated and not going to hold up for an adult reading them for the first time in the 21st Century without the benefit of nostalgia.
But the same could be said of almost every children's book she reads, so it's likely just that The Famous Five spend their summer holidays having fun adventures without taking their parents everywhere at all times, rather than studying all summer in full view of mummy and daddy every day, like Ruby does. They also put themselves at risk to help stop crime, save other people and better their community, so Ruby clearly couldn't relate.