"She also shifts a LOT, no matter how much I tighten/loosen her. I feel like I readjust her constantly. She is also EXTREMELY itchy to me, and I'm not really sure why. I've been wearing her for a while and she still just itches. "
There are products you can use which will help keep the wig in place and also eliminate the itchiness that it sounds like the lace front is causing you. I use a couple of different products for this - Got2B Spiking Glue (which you can get at Walmart, Target, and Amazon) which offers quite a good hold. You can also use the blue lace tape from Jon Renau. This stuff works fantastic - it is only the backing that is blue, the tape itself is actually clear. The Blue Tape is really good for securing the front and back of the wig to your head and keeping it in place while also keeping the lace off your skin to keep it from scratching you.
Also, try looking into the Hair Grip because this is another product designed to keep the wig in place.
I hope this information has been helpful for you.