If the coach cannot make the camp mandatory (maybe due to the school district or because it is too late now, as she's already said it is not for this year), perhaps suggest to her that you give out DVDs with the material from camp that needs to be learned before the start of the school year. Those that choose not to go to camp will still be held accountable for the materials, and it is up to them to learn off the DVD. Have a materials quiz at the first practice back..... something is called out and the coach can tap team members who know the material perfect to sit down after 2-3 repetitions, with those that don't know it having to repeat it until it is right (if it is still not right after numerous times, they don't get checked off). Those that don't know their stuff do not get checked off, and will get demerits/consequences/extra conditioning, etc. etc. Additionally, they will get tested every practice until they get all of their materials checked off (each practice they don't know their stuff = increasing demerits/consequences). A good idea to pitch to your coach, so those that do the hard work to learn over summer don't get punished for those not working as hard and you don't waste time reteaching.