Just looked this up on their site and found it says available in 4 sizes, but the drop down is missing large, as you said. I wonder if they just don't have any larges in stock right now? Regardless, I would probably go with an extra large anyway. It might seem big, but because of the Velcro, you can adjust it smaller. You would have a difficult time making it bigger and have it still be positioned correctly and effective. You said your heifer is 15 months, so you will probably be showing her for a few months yet, maybe even into the winter show season. She is going to keep growing, especially if she is bred and will have no issue filling out an extra large. Also, a search on here will give you some threads about excellent tips on neck sweats, the sweat "potions" to go with them and how to use them. Best of Luck!
