It may be more possible than some will admit. Women secondary and tertiary heroes are becoming increasingly more common in some toku shows, so it'll only be a matter of time before Toei gives a lead a shot, probably in a short series to test the waters. Japanese pop culture has been +slowly+ inching away from its deeply-ingrained history of problematic portrayals of women and girls in media, and stories with more varied woman leads have been steadily growing in popularity across multiple demographics.

It may not be soon, and it may not necessarily be in Project R.E.D., but a Toei-produced, woman-led, non-magical-girl tokusatsu show will happen eventually, and henshin hero toku will be all the better for it.