
Try jiggling the training routine up a bit! My girl used to do this when I started training ehr to roll over, as it was always down-roll over-up! every time - so I couldn't put her in a down without her rolling over. If you introduce a "wrong" word, like "no" or, oddly enough, "wrong" :D, you can say it whenever she does something you're not asking her to do - say she sits then goes into a down, you praise for the sit then say "wrong" for the down; it may take a few goes, but she'll stop and start thinking "what's different? Why aren't I getting a treat?" Eventually she'll offer a different behaviour to try and get a reward, giving you the chance to get her to do something different and praise her for it.
Stick with it, it might take a while to make her realiser you're not that predictable! It will also free you from any un-removable behaviours in the future - for example, I once used dinner times to train my dobe to spin round, he got the routine, and now every dinner time he spins furiously until the bowl is on the floor, and I can't stop him!!