GSC Help -- Impressions rose steadily, then fell off completely

My wife has a lifestyle blog that she started running around Sept last year. She learned a lot and her google impressions steadily rose, peaking during the busy Christmas season with \~500 per day. The past few weeks, however, these impressions have gone to nearly zero and there are suddenly loads of legitimate posts that are "crawled--not indexed" (filtering out all the "wp-content" and erroneous URLs) with nearly no explanation of why. I understand things go up and down, especially around a season like Christmas, but this seems like such a sharp drop that something went wrong and we're unsure how to fix it. Luckily, she's still getting loads of clicks and impressions through Pinterest, but Google doesn't seem to like her site anymore. Is there anything you can surmise might be the culprit? I understand people get paid a LOT of money to manage SEO, so please believe me when I say thank you ahead of time for any pointers in the correct direction. We're unfortunately not in a position right now to hire an SEO manager.