Hello, I'm Dr. Deb and will do my best to help you today.
I'm sorry for this concern for Little Bit, the newest member of your family.
There are a few otc products which may help her if motion sickness is, indeed, her problem:
1. Dramamine (aka dimenhydrinate) at a dose of 3-6 mgs up to three times a day. One problem, however, might be the milligram amount of the tablets which I believe is 50 mg. It's going to difficult to cut these tablets into a small enough size for her...approximately 1/8th of a pill...but I suppose if you purchased a pill cutter, you might be able to.
Lethargy may be seen as a side effect as could dry mouth or urinary retention. Diarrhea, vomiting, or anorexia are less common, but have been noted. The sedative effects of antihistamines may diminish with time.
2. Benadryl (aka Diphenhydramine...note the difference between this drug and #1 above) is another anti-histamine which has been used as a motion sickness drug. The dose for a small dog like this would be 1/8th of a 25 mg tablet up to three times a day. The liquid formulation is distasteful for many pets and may not be accepted by animal patients but if the concentration is 12.5 per 5 mls (the most common form), then her dose would be 1 ml or about 1/4th of a teaspoon at one time.
The same side effects as I listed in #1 might be seen.
3. Pepcid AC (aka Famotidine) can sometimes help with general nausea issues but isn't as effective for motion sickness.
The dose would be 1/4th of a 10 mg tablet twice a day.
There are other drugs such as Cerenia but they would have to be purchased from a vet.
Since dehydration is going to be a concern in such a little dog, offer her small amounts of pedialyte every several hours.
Low blood sugar is also a worry so rub pancake syrup or honey on her gums if she won't eat it every several hours as well.
I hope this helps. Deb