It would seem so at first, but she was obviously confused about the severity of the situation
Note the message where Bella first told her about the incest, she says she hopes she will distract chris from barb, yes but then she talks about how barb groomed chris
Then she was corrected by Bella that CHRIS was the one that groomed barb and she freaked out "he's grooming HER? WHAT?"
Soon after that, Fiona received a 9min edited version of the call from Bella which she subsequently leaked against Bella's instructions
Fiona is definitely gross for still wanting to be with chris after thinking he "consensually" or was groomed into fucking his mom, but I don't see how she can be blamed for caring more about fucking chris than barb being raped
As far as we are aware with the current info, after she took time to process that her idol she was obsessed with raped his mom, she was the one that leaked it because she wanted to, in her own words "do the right thing" even though she was admittedly afraid of what she got herself into
Fiona's autistic and dumb as a brick but I don't think she was malicious from the current information we have