Kudos to you for being there for her!
I should say that drastic improvements in 1-3 months may be the experience that some people have had, but it is not something you should use as a measure. I've been in EMDR for a year, and old forgotten trauma is still coming up. I know myself much more, I understand where it all comes from, and I've learned a lot about understanding when I'm in a trigger and how to get out of it. So there have been a lot of improvements. However, things my partner says can still trigger me quite strongly, and I can still emerge from therapy sessions feeling intense things that it takes a few days to process. Everyone is different, and people progress through EMDR at varying rates of speed. I think there are many on this board who've been in EMDR for a long time. The preparation phase is the most critical, during which the patient is learning how to be grounded and stable as triggers come up, and this can take some time. While it's probably the scariest thing I've ever done, EMDR has been incredibly valuable and I've definitely grown and strengthened emotionally from this therapy. Good luck to you - she is lucky to have such a supportive partner!