...maybe. But I think she's a little too pretend clever and not enough real clever (also too much crazy). Like planting her husband's fingerprints at the scene, etc...I get what she was going for, but it was a huge risk. I'm willing to accept what you say is a possibility, but I think she was too wrapped up in what she was doing to think things like this through.
Watching the movie again (which I did yesterday after a being over a decade removed from the first time), I paid more attention to her reactions. I think that whole scene in which she asks about them looking for the murder weapon was about the fact that it was in the basement (also a convenient plot device). Don't forget she WANTS him to realize she did it, so the more evidence that piles up the better (from her perspective). I think she knew all along she had a fail safe should something go wrong (her confession), so she was willing to let it play out. But again that's just my opinion, could be interpreted more than one way.