Hello there. My name isXXXXX and I am sorry to hear about Lizzie and her fleas. Comfortis will kill all fleas on her within 4 hours and will last up to 30 days. So depending on where she caught the fleas then you may be still seeing them. Fleas do not actively jump off animals onto another. They will drops their eggs which hatch and develop in rugs/carpet/yards/blankets etc. Then those are the fleas that will jump onto animals. the life cycle can take up to 90 days to break so once you see fleas on an animal they should be on flea protection for at least 3 months. They will not lay new eggs during that time since they are dying off. Also you will want to vacuum any carpet she is on or near, wash beds or blankets she lays on or near weekly. This will remove any eggs or babies that may be left behind. You may see the black spots up to 90 days depending on where she picked them up and their population. If she picked them up at the vet and they did not have time to lay any eggs in the house then you should not really see the black spots for longer than a week or two. They will go away faster if she is combed and bathed. The white flakes are from dry skin and can be helped by giving her omega 3 fatty acids (fish oil) daily on her food. This is really common this time of year and not likely related to the fleas. But definitely stick the the comfortis and this should take care of the fleas and start her on a fish oil supplement. you can get this from your vet or any pet store. I hope this helps and I hope this makes sense. Please let me know if you have any additional questions or concerns. I would be happy to help. Please do not forget to rate my response so I receive credit for my time. Thank you!