I'm sorry you're needing to deal with this. I've had several root canals and crowns and they're expensive (even as noted, with insurance) and no fun. Typically the endodontist does the root canal and the dentist the crown, in my experience, in 2 steps -- a prep to fit the crown plus a temporary crown, and then a permanent crown, which can be either ceramic or gold. The latter is more expensive and doesn't blend in, but more durable -- mine have been on rear molars and I've opted for gold.
I think the first question I would ask the dentist/endodontist in your wife's shoes would be whether this work can be spaced out over several years. If her teeth are abscessed, the answer is clearly no, but if the damage is less invasive/obtrusive, that may be possible -- the advantage of course being that this allows more dental coverage to kick in (assuming her policy like mine allows $1K per year). It also allows you to use flex money (tax sheltered medical expenses) if that is available through either of your employers. Though an alternative strategy would be to get it all done in the SAME year and see if that qualifies you for reduced taxes (you can deduct a portion of high medical/dental expenses, I think it's the amount that exceeds 10% of your AGI).
At least in the state that I live in/system I'm part of, crowns can be billed either when they are fitted (prep appointment) or the time that they are "installed." This can help with spacing the expenses out, if that turns out to be a goal.
Your wife may also want to talk to her dentist about whether she'd benefit from more frequent cleanings. I too have baddish teeth and my dentist recommends every 3 months. I've read up and this seems to be backed by the literature -- some people are actually OK with once-a-year cleanings and others benefit from more-frequent-than-every-6-month cleanings. Seems to me the former like to wander around telling those of us in the latter group that if we only tried harder ... but this relates to things like mouth chemistry (Ph and such) and enamel consistency and is not 100% within our control, as you clearly know. Personally I've settled on once every 4 months as this means my insurance covers 2/3 of my yearly cleanings and I only have to cover 1 ... and the gap between cleanings isn't much larger than what my dentist recommends -- or so I tell myself.