She will be issued a laptop (which will eventually be paid for by her over time and interest free out of her cadet pay). It is not necessary (nor preferred) to purchase one prior to reporting. There are several requirements that the machine must meet in order to have access to the government network (and she will have on campus IT support as well) - so best to let her use the system which is already in place to support her.
Please read the Parent Handbook and Cadet Handbook. I can't stress this highly enough. Every year we see similar questions on this forum and in the Facebook groups that can be answered by reading the information provided. On page 6 of the Parent Handbook it states "Please note that every cadet will receive a laptop computer before the academic year starts, even if they already own one. Therefore, there is no need to purchase a computer before reporting!" Cidgrad 130 is correct about the computer specifications and the government network. If something is not listed under required items or optional items, do not bring it on Day One.
@esteller1, if I remember, your DD is CGAS, not SWAB, correct? There might be a confusion because of that. I don't think others realized it's for CGAS just reading your post. Their Cadet handbook/instructions and your Scholar handbook/instructions are similar but different. 'Hope this clarifies what others said about not needing to buy one.
SWABS will be issued new laptops, but CGAS will NOT be. You definitely might want to buy a cheap one for the year, but if your DD already has a working laptop at home, she can probably just use that until next year. No need to buy a new one just for the year. Know also that they won't be doing anything heavy-duty on laptops at prep schools. I heard you may even be able to get away without purchasing one (by using school's computer room) depending on the school. Once your DD is assigned to a prep school, the school should give you a school-specific packing list and instructions separate from the CGAS list issued by CGA. Each school will have a different list, so follow their list. Send her laptop and everything else directly to prep school later, not to CGAS summer. If you haven't already, it might be helpful to join the USCGA Scholars Program on FB to ask CGAS specific questions there. Even if the school says you can use their computers, the kids would know better how available they really are.
When my DS was sent to GMC a few years back, we probably got him the cheapest one they had at Costco. It literally broke down in a year, but he did just fine with it until his 4/c year. Going back to your MacBook question, it'll definitely work, but remember that she won't be able to use it next year after such a big investment. (Unless you want to take it from your DD for yourself next year.)
What Blueman said. Our son went to MMI. Since he was looking at engineering, and while an appointment is likely (but not guaranteed), we actually bought a high grade PC laptop suitable for engineering if he didn't go to CGA. He did, and got his issued laptop. We use the other one at home (score!). He graduates in 3 weeks. The issued laptop is barely going to make it to commissioning. He asked for a new one as a graduation present, and we gave it to him early so he could get it set up before he goes to the fleet.
As an aside, and related to what Blueman said, we packed got all the stuff he needed at MMI into three packages and shipped directly to the school. None of that stuff should go to CGAS Orientation.