stop at rest points where there are others stopped. period. parking alone is never a good idea, unless you're out IN THE MIDDLE OF NOWHERE, and the road you came in on doesn't lead to some weirdo cannabilistic cultist encampment 2mi down from where you are. those places probably DO exist...
so.... put the "crazy trucker following me for hundreds of miles just to assault me" attitude away, and use the brain God gave you. Even though I'm a 6'4" 300lb guy(ya I know I'm fat), I still don't park anywhere that there isn't a light shining on the car. I'm not scared, but just prefer to play it smart when I travel. Besides, if you get yourself a pair of those eye covers that you get on planes, it blocks the light out. Rest stops right along side the road are a great place to stay, generally free, and since you're a woman, generally have a toilet to use, so no hiding behind the bushes when nature calls .
just be smart, and think twice about where you decide to stay. and don't let fear grip your life. enjoy your trip!
-Dan
<EDIT> and if you're in California, DO NOT CARRY A LOADED FIREARM!!!!!!!!! it is a felony, and CHP doesn't like to find a .380 under the seat, no matter how "pretty and alone" you are. my uncle was CHP for 24 years, and he has some stories to tell, believe me. you don't want to have that ruin your trip. pepper spray works well, the bear kind is best, but can be a bit unwieldly. a big heavy baseball bat would be best. HICKORY is still king for personal defense IMO. and ALWAYS have your cellphone on. ALWAYS....
-Dan