Except they're not quite equivalent: 
Zille tweeted comments that were thoughtless and perceived to be racist, thus bringing the party into disrepute, Ntuli simply 'liked' someone else's Facebook post - she never posted any comments herself. I'm not sure how someone 'liking' another Facebook post can really be compared to effectively claiming that 'colonialism wasn't all bad' (and it doesn't matter if Zille had a point or not in claiming that - it's about the perception she created that senior DA members are racists)
Sure both were stupid, and both deserve some form of sanction, but not necessarily the SAME sanction.

And the article suggests that 'Ntuli faces potential expulsion for liking a Facebook post criticising (Zille)' - if she is expelled for simply liking a FB post, then Zille should be fired from the party too, because her tweets did far more damage to the DA than Ntuli's simple 'like'...