This question is a mix between the usage of 侮れない and the usage of なかった instead of ない in the sentence
The usage of 侮れない like in the example below seems to refer to one who you cannot make light of,be unprepared against and so on. The kind of sentence below is what I would expect when someone is fighting someone,playing against them in a game/etc and you had the impression they would be a formidable opponent and then they did something that made you think the below.
But then here is where my question comes in. How is the た form used in these sorts of usages? Because surely a "past sense" interpretation doesn't make sense to me. Does the utterance(in meaning) mean that:
1) She is someone who is 侮れない
2) The た form in this case is used to represent that she was already 侮れない before this action and he has just realised this by her actions/words
I'm sure there's some more points here, but can anyone clarify this for me? I suppose this is similar to how when looking for something and then they find it they would say いた. Or perhaps if someone heard sounds and was wondering who it was and then realised who it was then they would use だった but if they came across them normally they would use だ/じゃないか/etc