Did you discover why she bolted on you? Do you know what training she's had in the past? How long have you had her, what have you done with her? What problems have you had? How is her back & saddle? How does she behave away from her friends when you're on the ground with her? What's she like in her own environment? How about strange environments, like trails/new experiences? What's her bodylanguage like when she's being 'barnsour'?
I ask the above because depending on your issues, using a bit of itself may not give you more control, and using pain to control & force her will probably lead to her becoming more 'barnsour'. Horses are herd animals who don't generally feel safe unless they're in the presence of a trusted, respected, considerate leader. Therefore, when we take a horse away from their herd, if we want them to be happy & confident, you must first establish yourself as that worthy leader.
Another big reason for horses being 'barnsour' is that people 'work' them. If we want the horse to willingly leave the pleasant surrounds & company of the barn, we need to present that 'work' to them in a positive way. Play with them rather than work.
Your question no.2 ... I would personally first establish the relationship & control without a bit, so that I could use it for communication, not for pain/control. But anyway...
It's a good idea to get her good at everything in a pEn or arena(eg. safe area) to begin with, as you're doing. This is mainly so you can *ask* her gently with your body & reins & persist until she stops, rather than having to use force because you can't safely allow her to go. Do lots of figure 8s, stopping, starting, turns on fore or HQ, backing up, etc. Get her softly reliable before doing the same exercises in the open, somewhere that she is comfortable, such as near the barn, in the paddock, whatever. I'd also take her out on lead, using approach & retreat tactics if she's nervous about going out, getting her reliable & confident with you before attempting to do this on her back. I'd also start out riding with other people before going out alone.