I have been a solo traveler for 26 years so far.
Going solo should not be a gender issue. If she builds the needed skills and support system, she will be able to travel wherever she wants and with or without whomever she wants. She can start now with small local solo trips. She's got plenty of time before the big one.
My first question to her is, does she really really want to go west? If it's an "everyone should go there" thing, perhaps she should wait until it's an
I'll just die if I don't get to go there" thing. Strong motivation can help a lot in overcoming anxieties.
She needs to be familiar with her rig - park it, set up camp, dump, etc. She needs to practice at least mentally some scenarios and learn what resources she can call on to help in times of trouble. Flat tire? Breakdown? Illness?
How will she call for help? Phone? Satellite messenger? Get the equipment and practice with it.
She needs to not be prey. Not be too needy. Predators go where prey is. If she is confident in herself and her vehicle and her wish to make this trip happen, she will have much happier experiences and memories even if some of those memories are about the time the water pump went out in Kansas City and I had to camp out and wait for parts and I met these nice people and...
Happy travels to her!