At first despite her situation mc is smart however this past chapters she's kinda giving t...

Based on how FL was pretty smart as a kid (which led to adults calling her creepy behind her back, which she overheard, and was the whole reason she started being a hikkimori) but she barely had any social interactions, except with her family and servants, she's probably like this because she was unable to develope her smartness properly. She lacks the experience to be completely smart all the time, but at the same time she was also smart from the beginning so she's not completely dumb. Is what I think.