My 2 year old daugther has strep throat and she is on antibiotics since sunday, 3 days ago. she has red gums too, is it part of the strep? thanks

Could be but: I would not assume that is the only cause of the red gums. You should have your daughter seen by a dentist as well, especially if she has never been. Make sure (though possible uncomfortable) to brush her teeth and gums well, even if she fights you. It must be done or it will only get worse. Not fun given her situation but important. Good luck.

No : I may be due to change in her oral flora including a yeast infection or a virus she has acquired.

Yes could be: Yes the same strep bacteria in the soft palate / tonsil area could certainly find its way to the gums especially when someone is tired and feverish and do not feel like brushing. It could also be a different bacteria due to immune system being stressed and possibly a strain of bacteria not being destroyed by the antibiotic remember to wash hands, disinfect tooth brush and do not touch your eyes af.