I agree with Tallchick. A new sewing machine that has loads of features is much like buying a car, you need to test drive several and see which one has the features you like best. Additionally I can't emphasize enough the need of good dealer support when purchasing a high end sewing machine. Most dealers will include, free of charge, classes to instruct new buyers how to get the most out of their machine. I would also encourage you to search reviews posted on line for any machines you are considering. There are many forums and places on the internet where people post reviews and comments about particular brands and models.
This is a fabulously generous and thoughtful gift idea but it would be much better for you or another family member to give her options and take her shopping. IMHO with a $6K price tag there are many, many machines out there that may have better options for a quilter. Personally I would be looking at Bernina but I am biased.
Edited to add, if she is sewing on a vintage Singer she may be completely content with that machine and want something with a larger throat for quilting, like a sit down midarm. Or if she is mostly interested in the embroidery features there are loads of models that do exquisite embroidery in that price range.