Do you take Marley on shorter car trips and does she throw up then as well? I think sometimes it just takes the pups a while to get used to the motion of the car. Paddington vomited quite a few times when he was little but has since outgrown it.
Make sure you put a towel under Marley in the car. Also bring a spare towel, paper towels and plastic bag just in case! We were caught short or one or two occasions which was not fun.
I agree. It was REALLY important to me that my dogs be comfortable in the car, because I am in the car with them several times a week for training and trials, and they also travel with us on vacation with our travel trailer...There are days that they are in the car for 6 hours or more with intermittent breaks.
So I was VERY sure to start them out with TONS of short daily rides when they were young. And as often as possible, these short rides ended someplace "fun" like a play date, training or a trip to the ice cream stand!
I think a lot of car sickness is just lack of practice and can be dealt with through more, short, fun exposures.
OTOH, I DO know a couple of people who DO travel regularly with their Havanese, and through luck of the draw, ended up with one that just gets carsick... no matter what. So with those dogs, they do medicate them, either with Cerenia or the non-drowsy form of Dramamine (check with your vet on dosage) and make sure they have the supplies along that Paddington's mom mentioned. (plus extra crate pads)