Digi looks very Border Collie to me... at least, her fur does, especially her ear fur. Lots of BCs with feathering around their ears get mats. The key is keeping up with brushing her - on a daily basis during shedding season, which is right now.

I start with an undercoat rake, then a slicker brush, and finish with a pin brush. It is VERY important to acclimate your dog to brushing, particularly in double-coated breeds. She should be getting excessive amounts of praise and treats when the brushes are even in sight, and you should be brushing her as frequently as possible to teach her that brushes are good. Procrastinating on the brushing will result in even more mats, discomfort, excessive shedding, and unhealthy skin & coat. It looks like the hair on her ears is very silky and whispy... that will mat up very quickly. I would regularly brush the hair behind her ears, and when you spot any matting, spritz it with conditioner and use your fingers or a comb to gently loosen the mat.