In the sentence 'I said she has a great job that pays well.', you are using *immediate (or informal) reporting* and telling us what you told Sarah.
Instead, if you say, 'I say she has a great job that pays well.', the 'I say' means it's your opinion (that she has a great job that pays well) just like 'Sarah says' means that it's Sarah's opinion (that she wants you to get a job).