Cautious, why are you so adamant that this sentence has come as some kind of unexpected, unpleasant surprise to Cressida? It really didn't. When statements reference 'injustice' it doesn't mean that the sentence itself was unexpected.
Just in the years since the gantry-climb, JSO activists have been arrested, worn tags, faced deportation, spent time as remand prisoners (including CG herself), and served lengthy custodial sentences. In a hardening political climate, and in the face of new public order legislation, activists were aware of new precedents for long sentences being set as well as the maximum sentence length.
JSO isn't some kind of shady, secretive outfit: anyone can sign up for an introductory zoom call via a link on the very public website, where, incidentally, they also publish details of activists' arrests, court appearances and sentences alongside campaigning successes such as acquittals, releases from prison and, most importantly, policy change.