SF didn't campaign at all against Brexit. I think SF would be delighted with the hardest Brexit possible and I think all their actions show that. However they can't say that and it's important from their perspective that the DUP and/or Tories take the blame. If they could they'd blame the Irish government too.
The blame game is an impossibility for most parties as they have not the support of the toxic British media on their side and SF would prefer to see a non Brexit which coincides with the wishes of their electors....end of.