In alt.aquaria Jeff wrote:
I have two female bettas. Males have the long pretty fins and females have
the short fins. I'm not an expert and I too have been asking questions, but
from what I have gathered in the past three weeks is this. Males will kill
a female as well as other males. Keep a close eye on them. If you notice
any aggression, take one of them out of the tank. You say one has strips.
My females get horizontal strips when they are stressed or in fear.
Vertical strips mean anger or ready to breed. First I had both of my
females in the same tank and the passive one had the horizontal strips.
Within one minute of removing the aggressive female the passive one lost her
strips. Maybe your female is in fear of the male...and rightfully so. Hope
this helped.

The OP is talking about the species Betta falx, which is a different
species than B. splendas, your typical pet store betta. B. falx are a
short finned, mouthbrooding species. I've never kept them to know about
their care though. I would suspect that like many species in the same
genus, that their behavior could vary drastically, so B. splendas
husbandry may not apply to B. falx.

I would suggest to the OP to look for a betta society, starting with the
International Betta Congress (IBC, http://www.ibcbettas.com/). Speaking
of which, here is their page on the species which shows several male and
female photos, along with spawning pictures:

http://www.ibc-smp.org/species/falx.html

It looks like the males have more colorful finnage from those photos.