Unlikely, no matter how you look at it, this kill is 100% premeditated because of the way travis was set up. There`s also the fact that she`s quite familiar with the set up, being a victim JUST like that back in Season 1 and Dan the dentist was wrapped in plastic in a similar way, who by "coincidence" was found by Dexter, i`ll be surprised if she buys his story of defending Harrison.
I think the whole love thing was not done so that she`ll forgive him by the first half of episode 1, i think it was done so that the blow of knowing hits her harder and harder it did, Deb is now broken beyond repair. Can`t wait for next season.