isDigit() is in the header file WCharacter.h. This is currently not included in the ShieldBuddy but we will add it in the next release. In the meantime, add #include "Wcharacter.h" to your sketch and copy the attached Wcharacter.h to C:\Program Files (x86)\Arduino\hardware\aurduino\aurix\cores.
The serial port (and stream) functions in the ShieldBuddy are based on the Arduino Due. The parseInt() is a new function which we have not added yet. You could try adding the attached files to C:\Program Files (x86)\Arduino\hardware\aurduino\aurix\cores like you did with Wcharacter.h. This might work. We will fix this in the next release.