I couldn't tell whether the last line was supposed to be "I'm not happy about this at all" and thus be a really harsh rejection, or "You certainly don't look happy." (In Japanese, you can drop the subject of sentence if it's "obvious.")
It's more of her trying to deny being happy, even though she is (as evidenced by the happy giggling, then clearing her throat before fronting a denial).
Y'know, I think this and the other one I half-botched shows that I just don't understand the tsundere mindset at some fundamental level... not exactly helpful for translating love confessions.
Give it time. Things like this must be read with some knowledge of context, which requires time and experience in everyday Japanese to understand. Keep at it, and you'll get it soon enough.
I find it ironic how alot of Classic Marisa drawings make her "Older" looking than the Window's Marisa we have now in some twist of fate. That's not to say I havent seen the obvious ones that make PCMarisa Loli-height, i've just seen more "Adult" Marisa in Purple form than i have Black/White form.
