When you collect hair for braiding it does need to be tail hair. If mane hair is long enough it can be used for tassels. Ideally the horse's tail would be clean and brushed out to start with.
Try to find the longest, most consistent (length) hairs from the end of the tail and cut those hairs close to the tail bone. Only about a pinky-sized hank is needed. Hair can be taken from a few different places to make it less conspicuous. The hair needs to be twice as long as the finished project.
The cut ends should be pretty even and a rubber band applied as soon as possible to keep them together. If the hair is not already clean, it can be cleaned with regular shampoo. No need for detangler or conditioner, just shampoo works best. Hang it up to dry, then that "pony tail" can be put into a ziplock baggie for safe keeping and mailed. It should be not braided or wrapped up wet as that can cause the hair to kink.
If your necklace or bracelet develops some stray pokey hairs they can be carefully trimmed flush with fingernail clippers.