There is nothing illegal about changing your status from salary to hourly. In fact, if your job duties do not qualify you to be considered exempt, they may be required to make the change. All employees can legally be paid on a non-exempt (hourly) basis. Not all employees can legally paid as exempt (straight salary).

Unless you have a bona fide contract or CBA that expressly states that you can never lose benefits, she can add, subtract, or change your benefit platform as she finds appropriate.

However, before I comment on changing the start date, I'd like to know what her reason is for making these changes.