While this product is very safe, the only disadvantage with it is that it may not be effective.
The unfortunate reality of your situation is that the only way to *make* an animal sleep who doesn't want to is drug her with anesthetic agents. If that's truly what you're looking for, I'm afraid there's no escaping the fact you will be disappointed. Without an anesthetic/tranquilizer, there is no way to force an animal to sleep when they don't want to, especially in the face of an alarming or stressful stimulus.
Additionally, anesthetics and sedatives are dangerous things even under the best of circumstances. Unfortunately, the only people who have the training and experience to manage a patient of any species who has been anesthetized is a medical or veterinary professional. We are prepared to deal with the complications of anesthesia like not breathing, low blood pressure, and even cardiac arrest that can occur when using an anesthetic. That's why your vet cannot just send you home with something to give her to make her sleep. I bring this up because I want you to have a full understanding of what you are asking for. I completely understand your desire for something to make her sleep during this trip. I just want to be sure you understand what it would take to do that.
In the meantime, let's be hopeful she responds well to Rescue Remedy. It's worth a try, and you can rest assured it's safe.
Another helpful hint that has been passed on over the years is that some cats who panic in a crate will travel well in a pillowcase.
The bot***** *****ne is that we prioritize everyone's safety here. We don't want you getting hurt trying to transport her, and we don't want her to get hurt in the process either.
Perhaps there is a veterinarian in your area who does housecalls and would be able to provide additional sedation for her. I know that if you were in my area I would certainly do the best I could to help you transport her without anyone getting injured.
I hope this information helps.