I think she'll end up needing two, if not three yari. My wife is about 6'1" and looking for the emitter to be around chest or shoulder height
That's closer to a naginata than a nagimaki. Traditionally, the length of a nagimaki handle is the same length as the blade. The Yari extensions are 15", vented couplers are ~1.75", and the Initiate v4 is ~9.875". So you're looking at ~26.635". With a 32" blade, you'd have about 30" of usable blade (as about 2" goes into the emitter). Short of a custom blade length, that's probably as close as you're going to get to that.
If she wants the emitter at shoulder height, then I'm going to guesstimate that at about 60" (5'). So, 3 Yari (45") + 3 couplers (5.25") + Initate v4 (9.875") = 60.125", or just about what she wants.