Dog seems more cautious after spaying

[LinZ]

I know I mentioned Nikki in a couple of other posts here concerning her recent spaying, but since she's come home, she seems to be barking a lot more, mostly at nothing.

Before she would yap only when she heard a car drive by that she thought was entering the driveway, but now she barks aggressively for no reason, and will sometimes do so at the cats, but she has never hurt them in this process.

She's been home over a week now, so I don't think she's still getting used to the house again. Any ideas as to why she might be acting so overly cautious of her territory?

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LinZ - sometimes wants to muzzle Nikki