hi there, welcome to the forum
lots of support here!
while my bf was in rehab i would send him letters/packages from time to time. notes, pictures, gag gifts and comfy clothing. he told me that they would go through the package with him and give him everything that passed inspection. nothing i ever sent got denied. i don't know if it is different where your gf is? you can always call and ask about protocol.
i know how tough it is, esp when communication is so limited, but it will get easier. this will become a stress relief to know that she is safe and on her way to a healthy life. my boyfriend would make phone calls very short, one because there were many people waiting to make calls, and also because it was hard to hear the voices of loved ones. he told me that although he wanted to talk to me and see how i was, that after hanging up the phone he would always feel really bad because he just wanted to be home. i don't know if it will be the same in your situation - but i understand where he was coming from.
i hope that you are able to take this time and focus on your personal happiness. relationships with those in active addiction are very draining, i know from personal experience where my boyfriend was an iv opiate addict. only two healthy people can have a healthy relationship. your gf is taking great steps towards her recovery, that is great news. keep in mind that the process of recovery is never over when it comes to an addict, it must become a way of life.
you have picked a great forum, make sure you read around there are so many stories and an enormous amount of support here. those of us with an addict in our life (whether active or in recovery) carry a different kind of weight on our shoulders and must learn how to carry the necessary weight and how to release the rest.
again, welcome and i hope that your gf stays on the road to sobriety