Sorry to hear about your daughter. Seems like I've had a very similar GBS situation (as does someone else on the site that I talk to....almost identical situations for us). I was diagnosed in early December 2014 and received the 5 day IVIG treatment in the hospital, after which I felt like i was steadily getting better for a month. I thought I was out of the woods and this wasn't going to be to bad.
About 4 weeks after my treatment, I did have a relapse. I noticed the tingling/fatigue/pain getting worse, but the real sign my neurologist was waiting to see was if my coordination/balance got worse. Unfortunately, it did and I was given another IVIG treatment, this time over 2 days at home.
Now it's just kind of a waiting game. I feel pretty good now and my balance is steady, so that's good. The plan with my neurologist is to keep a close eye on it, and if I start to turn for the worse, I'll get another IVIG treatment. Unfortunately, that pattern can continue for a long period of time, but the goal is that the "good periods" after IVIG start to get longer and at some point, it sticks. The good news for your daughter and I is that she did react well to IVIG, so there's no reason to think she won't continue to. It's just a waiting game, which can drive you nuts. However, the guy that I've spoken with on the site had 3-4 IVIG treatments (the last in September I believe) and since then he's had a steady recovery and hasn't needed any additional treatments!!
Way too early to worry about CIDP. Sure that's possible, but right now, there's no reason to worry about that possibility. My best advice is to keep preaching patience.....and this is the hardest part, but try to roll with the punches. She might need IVIG 2 more times, she might need it 10 more times, or she might never need it again,. She's got age on her side, so hopefully that helps!!
Give her my best and if she'd like to reach out to me directly, feel free to send me an email on the site and I'll send you my personal email. I've found it VERY helpful to have someone to talk to that's had a very similar experience. It's much more difficult to identify with patients who've been in the hospital for months, on ventilators, in comas, etc. Those individuals have such a bigger hill to climb, than the lucky one's who had more mild cases.