First of all, congrats for not doing what many guys do, which is take her out on your 90-liter board in 20 knot wind with 6-foot high boom, and then revel that the learner fails... the macho thing. Seen that soooo many times.
And then the usual advice... the first few times go out in perfect conditions, that makes it more fun and easier for everyone.
Namely and that is: on-shore or in conditions where she gets 'deported' towards shore and not offshore. If any single advice goes to make it more pleasurable, then it's this one.
Low winds, none of that "let's go out anyways even if the wind is too strong". Better not go out than go out in bad conditions and you quickly waste your investment.
Shallow waters, sandy bottom: this is a nice to have, but people learn so much better when the bottom is in sight. As opposed to deep sea. It's a psychological thing, but whatever works. (By the way, after 25 years I still practice new freestyle moves in the shallows whenever I can. Falls are more fun, coming back aboard is easier, really helps!)
Right height booms: no higher than shoulders. Sooooo many make that mistake of not adapting the boom height to the learne,r and you see them struggle with way too high booms. This is esp. true in lower learning winds. One can play macho and have 8-foot high booms when one is pro. As an aside, lower booms for learners makes it easier to pull the rig out of water (lower center of weight).
Another advice: a little bit at a time. Many people stay out for 3 hours at a time on the first outing, frustrate and that's it. I find small chunks of 20-30 minutes max, with a little rest and play, is more productive. (Here again, same for practicing new moves, BTW.)
Again, congrats on your approach and good luck! She's undertaking the best sport in the world, but am preaching to the converted...