If you check out the disABILITIES FAQs thread posted near the top of the board, it should answer most of your questions.
If her wheelchair looks more like a stroller, you may need to get a GAC because the CMs may not be able to easily recognize that it is really a wheelchair in order to allow it into lines (or see the current thread about stickers for using a stroller as a wheelchair).
If it won't get mistaken for a stroller, you may not need a GAC at all. Wheelchairs are allowed in lines without needing a GAC. The CM can see the wheelchair and know that you need wheelchair accessible access. If her needs are met by having that, you won't need a GAC. If she has other needs in addition, then you will need a GAC that covers those needs.