Might be! She's had strange mental blocks before, like backing up. She'll back up when you are in front of her or along side her, but she wouldn't back up when I was behind her driving. She'd just stand frozen and afraid. When she finally risked to step, she'd turn sideways, I think so she could see me. She wouldn't back up with me back there unless she could see me. I almost think she thought she'd be punished for backing into me.
On ponying, the funny thing is, if we turn her loose and ride, she runs along with us. If I could trust her loose on trail, she'd probably beat us to camp. ;~D If only we could teach her how to get the fire started.
Sounds like she didn't have a very pleasent life before she came to you. And horses have such good memories it's really hard to replace the fear with trust.
Maybe having your husband lead her right next to you on horseback to start. And try having him at her head for awhile reinforcing the commands when you try to drive her. Lots of patience needed I think.