It sounds like to me your mom was right on. Most people feel like they are pressured into doing work since they are there anyway. By your mom saying no and leaving this give you and her a chance to get a very needed second opinion. They gave her your X-Rays which is very helpful. When you go for a second opinion they can compare the x-rays to make sure if you really have five cavities or not.
Just a though you said this office was really busy since you had to wait so long. Is it possible that they got your x-ray mixed up with someones else ? They might have made that mistake if they were understaff and over booked. Mistakes happen.
Either way this does not sound like a dental office I would want to go to. Though I am not sure I would label them corrupt. If you really want know try doing a name search on line about this office and see if other people have anything bad to say as well.
Good luck to you