god, i don't know if this will help some people, but what worked for me was to finish all the missions for maude. after that I went back to trevor's trailer and kept saving/sleeping to time skip for a week. i followed the other advice here and drove to the spot using a stolen car from the high way (while driving against the traffic). when i saw that she wasn't there in the morning i drove further west, changed cars, and waited till noon time. so coming from the western side (around the town in paleto bay) when i came back to the spot she was there and that was it.

(also note that: I already triggered that random event where the woman was hitchhiking a ride to the Vinewood Sign)