Absolutely you are right to not perform the treatment. She is infectious and won't have her mask on for starters.
Secondly, anti biotics can cause skin to be so much more sensitive to anything.
Thirdly she may also have a slight fever and as she's ill anyway massage is a contraindication. Silly woman for not informing you beforehand as you have wasted her appointment due to her not telling you.
Also to note is that her lymph nodes will probably be swollen because they are trying to fight infection and shouldn't be massaged as they'd be extremely tender.
Always check your clients health status before their appointment as it will prevent your wasted time and effort in setting up and the client will not be left feeling disappointed.