Some of the birds around here have that kind of purple-tinged discoloration. Most often with the larger-combed Roosters, but I have seen it in pullets, and laying hens. As far as the cause, I can't tell you, but it seems it can sometimes be due to hormones, laying, high temperatures, dehydration, lack of oxygen to the tips, etc.
If the hen is acting fine, I would not be too concerned about it being related to heart problems. The degree in which the comb would be turning purple would be much more emphasized and the bird would likely be lethargic to a point.
My input. If the hen is acting fine, eating and drinking well, just monitor her.