Christ is born!
Immediately before joining the Orthodox Church, I belonged to the PCA. I hope I can be of some help to you.
most people in the PCA are quite theologically savvy and very interested in talking about theology. Calvin is kind of the archetype Protestant scholasticist, so many Presbyterians (the conservative ones, like in the PCA) emphasize understanding what their church teaches and why it is true. They tend to be both philosophically and theologically minded. I'm actually a bit surprised she isn't more interested in the theology of Orthodoxy, particularly if she is so drawn to the atmosphere of the Church.
For me, I wrestled for a long time with many doctrines of the Orthodox Faith, since they were in conflict with my Presbyterian conviction. However, I don't think this is a necessary step for many. Honestly, I don't think it was necessary for me, I'm just stubborn. Apologetics eventually came for me (I also had Protestant friends to question my thinking and what the Church was teaching me. I'm very grateful for them arguing with me about Orthodoxy, since they challenged me and made me step back and examine what I was doing. I still converted, obviously, in spite of their arguments...but it helped me make sure I knew what I was getting into), but what really converted me was constant attendance at the Divine Services, speaking with the priest to develop a prayer rule, establish fasting, etc. One day, I realized that I had essentially left Presbyterianism and had taken up the way of Orthodoxy. At that point I sought baptism and was officially enrolled into the catechumenate.
So, definitely speak with her if she's open to it, offer her these resources, etc. But, for me it was living an Orthodox spiritual life that ultimately converted me. I didn't figure out why
I rejected Presbyterianism and Calvinism for some time later. It's quite backwards, especially for such a knowledge-minded Protestant, but it worked for me. I found beauty and peace in the unsearchable depths of Orthodox theology...deeper waters than I could've ever imagined as a Calvinist. Once I rested there, I started making sense of it in my head...but my heart converted long before my head was ready.
So, when you two talk about Orthodoxy, talk about the services, what they're saying and why, talk about the importance of a private prayer rule, fasting discipline, etc. Help her to do
Orthodoxy...perhaps understanding it will come later. It worked for me.