oH GOD, a love rival comes up, we're fucked.
We all know that when a love rival appears, the relationship ALWAYS breaks apart or starts going through a war.
Here we go boys, fasten your seatbelts, this is going to be tough.
. . . You haven't read very many series if you think a love rival ALWAYS breaks apart the relationship or sends them through a war.
In fact, I don't think you've read THIS SERIES, which had a love rival show up just like, one story arc ago, with no serious heavy fallout.
I said her manipulation is harmless because she hasn't actually done anything to negatively impact Nanoha's relationship with Chidori. Her motive (steal Nanoha away) might be wicked, but I'd say it's better to judge someone by their actions. Has she tried to turn Nanoha away from Chidori? No. Has she interfered in their relationship in any way? No. All she's done is reestablished ties with an old friend. A result of that is that Nanoha has spent a little less time with Chidori, but that's just how life works. We each have limited time and have to decide how to allocate that.
no that's a smirk. it's a fairly common image to portray a smug feeling like that, where they just show the mouth, no eyes. and her being embarrassed for "accidentally sharing too much" is pretty commonly used as well. it's to make themselves look even more pathetic. and obviously she will try something or the author wouldn't have put her in with this set up at all ;) of course you can say don't judge people by what they haven't done, but this is a book, not real people, and authors often follow fairly predictable patterns.
They show the mouth to focus on the gesture. Hiding the eyes often hides the intent, but it doesn't read that way here to me. Also, smirks and smiles are drawn differently. A smirk is when one corner of the mouth goes up. In manga this is typically drawn with the mouth as a straight line clearly tilted up on one side, or a line that is clearly upturned more on one side than the other. Here you have a pretty typical, centered, symmetrical "U" shape. That's a clearly drawn smile.
It even has the word "smile" as a sound effect, although I'd have to see the raws to know if that's accurate. At the very least that suggests that the translator doesn't suspect anything nefarious in that moment, or they would have written "smirk" instead.