areyou sure it is thrush and not milk residue? if it is just the tongue and not the rest of her mouth i would say that is what it is.
Try a little h20 after a feed to wash away.

Otherwise make sure you are cleaning bottles teats and your nipples well with warm soapy water as this is where the thrush will thrive. And get some nilstat from you dr to clear it up.

But i would say it is milk residue hun!