I was an SDM instructor in the Army before it moved to Benning and I have a bit of advice:
I wouldn't spend the money on the ACOG unless you just want one, focus on irons, the ACOG is easy and they'll teach that. A 20" AR15, probably the FN rifle would be the closest to what she'd be issued. I actually was issued an FN in basic, NIB Colt M4's at unit. If she shoots the M4, the trajectories will be different than the 20". So not sure I'd buy this either. Her own pistol may be handy though, now and later.
What would behoove your daughter now is PT. The Marines will give her better rifle training than the Army, so I wouldn't worry about it. They'll take care of her. You could take her to a shooting instructor at a range, but that'll likely be derailed by Marine doctrine once she gets there.
If it was the Army and she wanted to be a good shot, I'd say yeah, get her own and practice now and later when possible because they have the blind leading the blind on the POG ranges, and a lot of infantry ranges aren't much better either. They'll still get her to where she needs to be for the job, but Army doesn't care much for marksmanship (in general) just volume of fire in general directions. If she's interested in serious marksmanship in the Army, she'll have to do it on her own time. Can't say how Marine MP's are to be honest.
Military also uses special targets and at certain ranges for their qualification and initial zeroing. The Marines may use KD ranges for this too, I don't know.
I think she'd be better off focusing on PT and getting mentally ready because like I said, they'll take care of her. If she has to shoot expert for her position, then they'll make sure she shoots expert.
Without the proper training she'll likely just learn bad habits on her own. Without someone teaching her with a military background and teaching it the way they teach it, it won't be of much help. Just trying to save you money. But I do think the pistol could be a good idea, especially with an experienced pistol instructor. She'll should be able to incorporate that into what she learns there too. IME, soldiers have less proficiency with pistols than almost anything else. They get carried and cleaned a LOT, but seldom used. MP's may be different though, they're more pistol oriented.
Again, and were it me, I'd do PT (lots and lots of running, because that's the number one thing that'll make her life easier when she gets there, period). Train to be a marathon runner, seriously, but don't cause any injury! Since she has time, she may want to talk to the recruiter about taking classes at the community college in the meantime. If she's working on her degree, she can continue that in service and apply to take some time off and finish school while in the military, graduate, then apply for OCS and end up an officer, all in a few years. Which she may not be interested in now, but will be if she stays in. Plus it gets school out of the way and it's paid for. The college credits may also earn her rank going in, as does completing certain tasks like a PT test, drill instruction, etc.; this does/did in the Army, don't know about Marines.
And tell her good luck! It'll be an adventure, that's for sure. It was one of the best times in my life coupled with some of the worst. I miss it.
