Foul odor is definitely a sign that something is going on. She could have a mouth infection, but if her saliva is thick, that could be the start of a respiratory infection. My cham's mouth has no smell and he also has no noticeable saliva, so that would worry me.
If you are very gentle, sometimes you can get a cham to open its mouth by pressing on either side of the jaw or stroking the chin. I have not had luck with either of those methods, myself. My little guy is crazy stubborn and only the vet can get his mouth open.
If it were me, I would probably take her to the vet, just to make sure. Catching things early is important. One of the primary defense mechanism of small animals is to not look sick, so by the time symptoms appear, the infection could be well established.
Good luck and keep us updated.