Hm, I don't know. I think if she seems fine throughout the day and night and has the requisite numbers of wet diapers, you are fine.
Sounds like foremilk....are you really confident that you are emptying your breasts when you nurse her throughout the day? Are you switching sides too often before letting baby empty one breast?
You can check with your pediatrician if you really want to.....or a lactation consultant, but she sounds normal. My son would go back and forth between green some days and yellow some days.
Is it a mucousy green? That might indicate a sensitivity to something in your diet...not as common as people think thought.
I can't imagine she's catching a bug....they can, but an exclusively breastfed baby at that age doesn't stand that much of a chance to get really sick.
My best, uneducated, guess is that it is a foremilk imbalance. Does she nurse in shorter bursts throughout the day and you switch her and maybe in the afternoon/evening she nurses longer or you are able to sit still long enough to nurse her, hence the yellow poops later?
Is it dark green or just that light green? It could just be her....that's still considered normal.
Good luck..probably all fine!