Could someone have taken her in? She is a very attractive cat. I have three just like her that I am fostering. Seeing as she is so striking it is possible someone may have decided they wanted her. Especially if someone has been trying to make friends with her for a while and finally got her.
Have you checked with any rescue groups that may be working your area? Possibly TCR. Maybe one of their trappers got her by mistake thinking she was a stray. Especially if they saw her on a regular basis. Even with a collar on.
Have you gone in person to the Humane Society and/or any other shelters to see if she was picked up? Not phoned, actually gone there? When you do ask to check the sick room and the feral room as well. Especially the feral room if you say she runs from strangers.
Have you gone out at night or early in the morning when it is quiet with a flashlight to shine into bushes, under houses, etc, to see if the light reflects of off her eyes anywhere? Have you taken a bag of her favourite treats with you and shaken it? Have all of your neighbours checked their garages and sheds to see if she possibly got closed in by mistake?
And, while you don't want to think of it, you need to also find out who picks up road kill and ask if she was possibly a victim. :sad: I know you don't want to think of it but it is possible. Are there dogs in your area she could have been attacked by, possibly badly hurt by? Coyotes? There are so many dangers out there for cats on the loose.
I am sending up an extra prayer tonight for yours and many many other lost kitties. Good luck.