Is the health benefit/caloric burn determined by mileage or by time spent cycling/effort exerted?
Does having a heavier bike that is more work to ride a better workout than a bike that rides smooth as silk?
I was answering this question with specific data to back up my answer.
I don't really care whether she buys a new bike or not. I wanted to answer the question she asked not give anecedotal evidence about whether or not a new bike would help her achieve her goals.