Well, it depends. Are you serious about trail riding? Do you want to take her out alone a lot, or are you content just waiting until you have a buddy? I know a lot of people who will only trail ride if they have someone else to ride with, and that's fine.
In any case, being able to ride alone is a good "skill" for a horse to have, and taking her out alone consistently will find her settling down. As with anything, it takes practise and consistency.
The best thing that you can do is make sure you are totally calm. I have found that 95% of all my troubles on the trail start on days when I'm feeling angry, nervous or frustrated.
I really like to bring along my iPod and speakers in the saddle bags and play music. It gives me something to focus on besides feeding my greenie's anxiety, and I have also found that the horse, too, seems to listen to it.
As for making her focus, quiet down, and get her attention back on you...you might not like what I'm going to say, but there's not really a whole lot you can do besides time and ride her a lot. When I first began taking my younger horse on trails alone, I was always so concerned that she wasn't focusing on me, so I'd make her do circles and serpentines and ridiculous shapes, and all it really did was make her more: "OMG!" If she gets really upset about something, I'll leg yield or bump with my legs to let her know I'm still here, but for the most part, I just let her do her thing. She still likes to look around, but I'm finding that she is settling down and the more I get her on the trails, the more relaxed she is with each ride.