I recommend a carrier that has enough space for the cat to sit up straight in, as well as lay down comfortably in while sleeping. Most carriers are not big enough to accomplish all this. You also want something where the cat can see out of multiple sides, and where the carrier has good ventilation. I think stay away from soft or hard plastic "windows" that show the cat the outside world without providing much airflow, and go towards mesh sides. My cat carrier has mesh sides and despite my cat's numerous attempts at scratching and biting on it for years, he still hasn't ripped it open, just some fraying in a few parts.
Maybe something like this could work: https://www.chewy.com/necoichi-portable-stress-free-cat/dp/146209
(Though personally I think it's too flimsy to be car-safe enough regarding keeping your cat safe in a collision or vehicle accident....but most pet carriers are inadequate.) Besides being seemingly large enough (possibly too large, but the size of your cat and the other things you need to fit into the car will determine that), this one seems nice because the cat could have the option for complete privacy with the mesh parts covered instead of exposed, which could help soothe stress depending on her reactions.
If you're sure the cat will pee inside, then do what Amy says and put a towel or pee pad inside the carrier, and ideally change it out as soon as you can. I know my cat really tries everything he can to not go inside his carrier, so I think it will very much stress your cat out to have to be stuck near it. Cats are very specific about where they want their scent and where they do not, and also in what forms.
Also, as someone else said, anxiety meds will be good, but at the pet store there is also some calming spray that should help soothe your cat as well. I'd spray all over her cat carrier inside and outside before she gets into it, and in the car near where she's going to be, and refresh every couple of hours or so. It also helps if you are as calm as you can be so she can see that from your perspective this is not a stressful situation.