is she shooting the ACC pro. if so its a 440 spine and should be pretty right on for spine. If her true draw is 27 inches her arrows could be cut a inch or 2 shorter than 28 if you are that worried about speed. Here in New England I wont have many shots over 40 yards so speed isn't a huge issue for me. my draw is 30 inches but my arrows are 29 inches. I have a drop away rest and the end of my arrow ( with out point or broadhead) is about an inch in front of my rest. that is a good way to get the shortest and safest arrow for your set up. Hope this hepls!!