Crash Rescue mission won't trigger with any of the 3 characters

There's a potential fix in this gamefaqs thread. They suggest that approaching from the east never activates her. Check out what they recommend.

I haven't messed around with the Epsilon program yet, so I can't help ya there, but for Taliana, I always find her around mid-day, early evening time. I've also noticed (at least for me), that approaching from the east never activates her, I always have to come around the western way. So, instead of going up the east highway, go to the other side of the map and try going all the way around Mt. Chilliad. She should be in the grass in the middle of the road, just before you come up on a tunnel.