My guess is she just isn't good enough. Far superior Hawkeyes (Logic, Doyle, Gustafson) failed to stick in the WNBA right away (Gustafson developed enough post-grad to make it). That league is pretty much All-Americans, or players with an elite combination of size and athleticism that teams will take on as a developmental piece. While there are more spots now (more teams, expanded rosters), there has also been a massive influx of international talent recently, so the pool has expanded more than the spots. Hannah was a very good college player, but that doesn't cut it. If she gets a shot, it will be via the Gustafson route: playing internationally and expanding her game.
Going into the season, I thought Hannah would get a shot with a WNBA team doing exactly what she did with the national team last summer: coming off the bench, playing great D and hitting the boards, and being an effective ball-mover on offense. She had a good senior season, but her FT shooting regressed (it needed to improve), and her ability to finish creatively around the rim improved, but not enough. Her assignment is the same as it has always been: get that FT% consistently north of 70, and figure out how to finish effectively over, under, and around taller players near the rim. If she can really grow those areas playing internationally, she is worth a WNBA shot.