Thanks for the additional information. It is helpful.
Shaking or trembling in toy breeds at a young age could be due to hypoglycemia, liver shunt, or a neurologic response such as a seizure. Trembling can also be a sign of pain, stress and cold. Hypoglycemia is low blood sugar and frequently causing trembling in small breeds. Feeding your dog smaller meals more frequently can help. If you suspect your dog is having low blood sugar you can put a drop of pancake syrup on your dog's tongue which should raise the level.
A liver shunt is usually a genetic condition. It is a condition where instead of the blood going through the liver and being cleansed, part of the blood is diverted around the liver resulting in a toxic buildup in the blood. You can read about these here: http://www.malteseonly.com/shunt2.html
Seizures can manifest as trembling and a dog may not lose conscienceness. You can read more about seizures here: http://www.marvistavet.com/html/body_seizure_disorder.html
You indicate that she just started sitting on your lap and in your bed. If that is the case, the trembling might be due to stress of fear. If seh is new to you or just being allowed on the furniture, it might be putting her under stress. She may not know that you are ok with her being up there and thus is worried. If this is the case, it should resolve with time alone.
If she was trimmed at the groomer, the groomer may have clipped her too short somewhere and she may be a little chilled but I would expect her to continue the trembling no matter where she is sitting. The same would apply if she was trembling due to pain. As long as she is eating, drinking, eliminating and moving pretty normal, I'd monitor her. If it continues to be an issue, then I'd have your vet take a quick look at her.
Of course, if she develops other symptoms have her seen earlier.
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