Needing some suggestions:

don't think contacting her thru here would be a problem.  I agree about bypassing the agent since you don't know if he has anything to do with her providing.

I guess I would introduce myself as the guy who is booking her for a shoot so everyone is clear and she knows who I am right off the bat.  Seems like that wouldn't be a big deal, but I know sometimes there is a lot of etiquette I manage to miss.

The reason I ask is that this will be on the model/provider's mind and I think she will feel creeped out if this is behind your wife's back, seeing as how she is going to be somewhat intimate with her.

Don't some providers have bookers, agents or others who also screen their PMs and keep  their TER ads and TER profiles updated?  

Oh, no, my wife is very much a part of all of this!  She's quite wonderful.  The shoot is just between the girls, but assuming they hit it off, I was interested in booking the model for some time with my wife and I afterwards.  All out in the open, so to speak.  I'm just trying to figure out the best way to coordinate both of those appointments, given that they may have very different individuals managing them who won't necessarily be working in conjunction and I don't want to speak out of turn or spook anyone.

Explain why you are doing so, and I don't see how she can be either spooked or offended.

Yeah!  I try to not take it for granted - very lucky, thanks.  Looks like once everything seems square with the agent, I'll reach out to our model on the provider end.  The good advice is much appreciated.

unless the agent acts as her pimp..there is no need to worry..just book it..

that provders generally require communication with the female partner prior.  Surprises of this nature have high risk of backfire.  The SO storms off, husband chases after her...  leaves provider by herself, no donation & a block of time committed.