Actually, it would be highly recommended to use phenobarb to taper off the benzos if you're addicted to benzos. I don't follow her logic in prescribing an addict their drug of choice (or a variant on it), given that an addict is unlikely to stick to a taper and more likely to eat it all in a few days.
You are very unlikely to have abused phenobarbital. It's just not recreational. Yeah, I know, it's a scheduled drug, and it'll cause dependence if used long term, but it's so ridiculously long acting that it's not euphoric at all. I don't think anyone becomes addicted to it, I mean, it's still fairly commonly used to treat epilepsy, I know a couple people on it, my dog used to take it, and none of them developed addictive behavior while taking it, something very common with benzos, opioids and other addictive drugs. Phenobarbital feels like being dizzy, hung over, sedated and maybe a little disinhibited. Feelings of well-being are not part of the equation.
Also, it makes perfect sense to use phenobarbital to treat benzo withdrawal. Both target the same receptor, and while they target different sites on that receptor, both increase the flow of chloride ions through the receptor pore. Phenobarbital will completely block the withdrawal and without the enjoyability factor, no feelings of euphoria, it's easy to stick to your taper schedule. You're able to dissociate the blocking of withdrawal and anxiety from the recreational effects of the benzos, helping to break the cycle.
Just my thoughts.