Do you have a specialist who works with gifted kids in your area? While I certainly think that's preferable, I don't think it is the only option if that's not accessible. As important is to get the kid in with someone who can see them soon and on a regular basis and that is probably going to be someone local.
It seems to me in this thread that you've describe a wide range of possible concerns (oppositional behavior, depression, attention, anxiety, challenges posed by a medical disability, need for greater independence, perfectionism, etc.) While giftedness may well be part of some of these issues, as many maybe related to her personality and medical challenges.
There are MANY good therapists in the world who are not gifted specialists. If you don't have the gifted specialist option locally I might think of instead looking for a good general therapist who gets along with teenagers and is a respectful, open minded individual. That is most likely not going to be someone who bills themselves as an ADD specialist. Especially given the particular considerations association with your daughter's medical disability, it is likely going to be the case that any therapist you choose (even if they are a gifted specialist) is still going to need to be open to adapting to learn more about her unique situation.
If you don't have a gifted specialist in the area, one option might be to travel and get an assessment and then pursue ongoing therapy locally. You'd then have the gifted specialist available to you as a resource as you attempt to tackle these concerns. It may be unpopular to say, but personally I am not a fan of assuming your child has SB scores in the 160s because she scores 99% tile on acheivement tests. Those are really different things. I have seen bright and aware parents totally get the level of giftedness wrong. As a general rule I don't think it is particularly important to get IQ scores at this age, but given the situation with her schooling it may be helpful to get this information.
At any rate, I think the biggest help is going to come from getting a really good therapist who can help her through the challenges and transitions that come with adolescence.
