Yes good females are very hard to find. Patience is truly a virtue in this case. Lol . For future "hunting", best look for a female first then seek a male for her - much much easier.
About rays; this is just an illustration
This illustration shows 8 and 4 end rays. Notice how each ray branches into 8/4 rays. That's what we mean when we say "8 ray" caudal. You need a betta that only branches into 2 or 4 rays.
The yellow female seems to be 2 ray - not clear because she is not flaring. Her caudal has rather round edges. Her dorsal may have potential - the front ray seems long and almost upright (thus when she flares it may be upright). Her anal is short (something you want in young bettas because they will grow faster/more than caudal) so it will be balanced when she ages. Her body is not symmetrical and not good topline. Further she has uneven scales (bumpy side body).