I agree...does she like a specific color? You can get some colors from factory kits and others from hydrodipping or Cerakote...
A better than stock trigger is always a good investment. I find the RRA two stage match trigger to be a great choice and the most affordable that I know of but you can always upgrade. I would add a rubber pad like the Magpul Enhanced recoil pad but not for recoil, a .223/5.56 doesn't have enough recoil to worry about, but instead to protect her shirt from the rough finish on the buttstock. I prefer the Hogue grip or the Ergo over a stock grip. I'll post some pics here of a couple of mine and maybe it'll give you some ideas of what she may or may not like. The color fill lettering can be done in any color at home and is a very inexpensive way to customize an AR.
This is my Colt LE6920...lot's of pink, I love pink, but with a little money you can do pretty much any color.
This is my Loki 6.5 Grendel/.264LBC. It's a Hogue free float forend, Hogue grip and a pink Magpul buttstock that you can't see. It has a RRA two stage match trigger. I prefer the Hogue grip over the Ergo but some people prefer the Ergo but either way the rubber grip is my favorite.