Interesting, I learned something. False pregnancy, also called pseudocyesis,
http://en.wikipedia.org/wiki/False_pregnancy can occur in females of many species, including humans as well as dogs. It's not well understood either psychologically or physiologically.
I just did a review of the literature. There isn't a lot of information about pseudocyesis in spayed canines. Most cases are in dogs that aren't spayed, however it seems as if there are many hormones that come into play, not just those that come from the uterus and ovaries. This was the one website I found that mentioned it can occur in spayed females, but unfortunately I couldn't open it.
FALSE PREGNANCY IN DOGS - Chinaroad Lowchens of AustraliaFalse Pregnancy (Pseudopregnancy, Pseudocyesis) Non-pregnant female dogs commonly ... and ovarian abnormalities, but it can also occur in spayed females. ...
From what I can tell, it usually lasts about 3 weeks, and can produce symptoms that would occur with a real pregnancy, like swollen mammary glands, weight gain, licking, etc. Is your dog doing any of these things?
Sometimes they treat with hormones, but it will probably play itself out without those (if that's what it is). Sometimes they give diuretics if the glands are swollen, but that would seem extreme. I'd probably see what the vet had to say and see what happens over the next several days to weeks. The literature says to discourage the behavior, but the mother in my wants to say let her have the toy if she likes it.

: I don't know, go with your gut.
