JK Rowling isn't feminist enough for feminist extremists anymore. She's being labeled a "TERF," or Trans Exclusionary Radical Feminist, basically a feminist who doesn't put trans women on the same ground as biological women.
e.g. a TERF might not be okay with trans women competing in women's sports events due to fairness concerns, or trans women being allowed in women's locker rooms or bathrooms.
Evidence of this seems to be predominantly guilt by association, for following "transphobic" accounts on Twitter, and not her own words.
Rowling has been seen liking transphobic tweets in the past, though at the time, her rep said it was the result of “a clumsy and middle-aged moment and this is not the first time she has favorited by holding her phone incorrectly.” Now, though, she’s gone on a TERF (trans-exclusionary radical feminist)-following mini-spree, meaning she’s choosing to introduce transphobic views into her timeline.
Rowling follows less than 700 accounts on Twitter, and she recently added the aggressively anti-trans YouTuber Magdalen Berns to that list. Berns, who has called transgender people “Blackface actors” has filled her YouTube account with videos like “There is no such thing as a lesbian with a penis” and “Misgendering is violence? Nah, mate!” and plenty of arguments over “genital preferences.” Her Twitter account is no different. It’s nothing but anti-trans bullshit.