CC is supposed to work within 5 days, it it's going to work at all.
Also, with CC, you go in at varying lengths of time to calm the baby until the baby gives up crying and goes to sleep, rather than just leave the baby to cry it out.
BUT
If you're baby is a "stress increaser" rather than a "stress decreaser" when crying at night, it may not work at all.
Did you try CC at night or for a nap? Babies will hold out a lot longer for naps and CC doesn't tend to work so well for daysleep.
Rather than rely on the long lunchtime nap, maybe see if she'll do a third nap between 1500 and 1600? Five hours is still a long time between sleeps for an 8mo, so perhaps she's overtired by bedtime, despite the long lunchtime nap.
My own experience indicates the gap between sleeps is at least as crucial (if not more so, sometimes)as the amount of daysleep.
My own DD is just over 8mo and she naps for half an hour at some point between 09.00 and 10.00 and for another half an hour between 12.00 and 13.00. I then take her for a walk in the pram from about 14.30 and she usually gets between 1 and 1.5 hours, waking no later than 16.20. Sometimes the last nap is shorter than an hour, but that seems to matter less than when she wakes up (ie, as long as it's after 15.30, she can usually make it to 19.00 okay).
I'm sorry to hear it's so tough for you. I hope some of this may help. Worth a try, anyway, if you haven't already!