@Ropoloid lol, making penicillin might be easy now because of the resources we have but it would be definitely more difficult in medieval times during a crisis. I don't even know if they have time to actually cultivate the mold cultures in the first place and even then you would still need to use specific measures to actually "harvest" penicillin.
The concept of using radiation to get rid of bacteria is fucking stupid as hell at first glance but, honestly it might've been the best immediate solution now that I think about it. Doesn't explain why Anna who doesn't know water magic can pinpoint the location of the bacteria though.