I would strongly recommend getting your dog to a vet, as it sounds like she may have ingested a toxin. While she was out it's possible she got into some sort of poison or chemical. Certain plants can have this effect too. In addition, it's possible she caught an animal that had been poisoned. Say your neighbor uses rat poison to kill off rats on his property. Now, a rat ingests the poison and wanders away. A little while later, the poison starts working and the rat gets deathly ill. Now, your dog comes trotting along and notices the rat. This sick, dying rat is going to be very easy to catch. And most dogs will go for it. And most dogs will eat it, in part or in whole. And then you end up with a sick, sick dog. It's possible she got hold of a pesticide, like a slug poison - the possibilities are really limitless. But these symptoms you describe are very concerning and I think there's a very good chance that things could turn out very badly if she doesn't get help very soon.
The tremors, staggering, foaming at the mouth, all means that her nervous system and possibly neurological system has been affected. So that means her brain, nerves, spinal cord, heart, lungs, and other organs - all this could be affected and sometimes, if treatment isn't given quickly, you can end up with a bad situation.
At this point, I would look into getting her into an emergency care facility asap. If your normal vet is still open, I would call and see if they're able to assist. If not, they can refer you to someone who can. Here's some things to monitor on her:
A dog's normal rectal temperature is 100.5 to 102.5 degrees Fahrenheit. Ear temperature is slightly different: between 100.0 degrees and 103.0 degrees.
Checking the gums is an indicator of your dog's circulation. If there's internal bleeding, anaemia, a disruption of normal blood flow, or serious illness, the gums will turn very pale, almost white in appearance. This means that the blood is not properly receiving oxygen or there's a loss of blood or red blood cells.
Normal gums will be bright pink to a pale pink. Abnormal gums are white with greyish, blue, or yellow.
Here is a link to a photo of normal gums:
Here is a link to a couple of photos of pale gums:
I should note that I've seen perfectly healthy dogs with gums that are slightly paler than those pictured in the "normal gums" picture, but there's always a distinct pink tone. For more information on checking your dog's gums, visit:
The normal heart rate varies depending on the size and age of the dog. A puppy has a heart rate of about 180 beats per minute. And adult dog will have a rate between 60-160 beats per minute. Small toy breeds can have normal heart rates of 180 beats per minute. The rule is the younger the dog, the faster the heart rate (for puppies). And the smaller the dog, the faster the heart rate. Normal pulse is between 60 and 120.
Also, you can check capillary refill time. If you apply firm pressure to the gums, the area should turn pale and then quickly return back to normal (you can try this on your own skin to see what I mean). If there's no difference, or if your dog's gums take a long time to return back to normal, there could be a problem. The gums should return to normal in no less than one second and no more than two 1/2 seconds.
I hope everything turns out for the best and I hope your girl makes a speedy recovery. Please let me know if you have any additional questions at all and I would be more than happy to help you in any way I can.