In some ways, this sounds like DD16. When she was young, maybe until age six, she would mix up opposites - hot and cold were the most notable mix up. She also either doesn't know or can't find some word she should know. I can't recall the word, but a few weeks ago, DD9 knew the word and said it, but DD16 could not find it (or didn't know it).
With the words like hot and cold, I think she always understood the difference, but it didn't come out that way went she said it. She is a very good writer, but her vocabulary is odd. She knows some "big" words and tested at a graduate level lexile in 8th grade. However, she just took the SATs (as a 10th grader) and critical reading was her lowest score (though still 94th percentile). I don't think anyone sees this as a problem because she clearly can compensate well. Someone gave me a name for this a long time ago, but the cost to test and confirm seemed high.
