...unsupported conclusions from a small sampling of data being filtered...
You left out the part where she openly admits ignoring some data: that there is femslash, but apparently it's not enough for her to think about, that there are happily-ever-after slash stories where the couple stays together, but she wants to focus on the ones where they don't, that there are lesbians and bi women writing slash, but she'd rather believe they are also just following the patriarchal prototype for artistic expression, in which art must oppress women.
There's a whole lot of "I believe this, ergo I will only address data that I believe supports this. All other facts are irrelevant." With the cute not-too-subtle submessage of "anyone who tries to mention other facts is a tool of the patriarchy."
I am happy to discover that some aspect of my sexuality is indeed mainstream and normal. It's a very reassuring thought. At least, "mainstream" as her type of radical feminists define the term. There's a part of me that suspects, however, that at the point where you've defined slash fic as "conservative," you've lost the battle for useful terminology.