IRCC probably won't know so work permit won't be cancelled. What would happen though is, she will face the choice to lie on future applications about that work experience or admit it. If she chooses to not mention and IRCC finds out, they will probably issue a PFL and then a ban for misrepresentation. If she admits it, it could go either ways.
Another thing to consider is, the income must be reported to CRA and then it would appear on notice of assessment. Now, if she doesn't report income, it will be considered tax fraud. So you are looking at potential tax and immigration fraud all over $600...
Actions have consequences. Hopefully, she makes better choices in future and not get shortsighted.