Did your vet look at Daisy's molars too? Or just her incisors? To examine a Degus molars, they most likely may have to be sedated, since most don't sit still enough to allow you to open their mouth and check in there. The molars continually grow as the incisors do too, and can grow spurs if the Degu doesn't keep them properly worn down. That can affect their eating if it gets bad enough.
So, depending on exactly how far the tooth exam went with your vet, they may or may not have been able to check everything.
I have only learned this stuff by having tooth problems lately with Imana. It has been a very interesting learning process.
If you Google "rodent malocclusion", you'll find lots of info about that, and you'll even find some photos of rodents who have it. There are many other tooth issues that can go on inside those little mouths, like root elongation, but malocclusion is the most common. It simply refers to the abnormal positioning of opposing teeth.
Sometimes, if they chew on their cage, or something like that, they can damage their teeth to the point where they just get a little off.
If you are still concerned about her, I would say maybe look for a different vet in your area who knows more about Degus?
I read somewhere that white teeth is a sign of weak teeth. That can be due to a vitamin deficiency, or something similar. That might explain why Daisy is having tooth problems right now - if they're weak for some reason. Has the color come back at all?