Forget phone calls and emails.
If you really want something, go to your client’s office.
Politely and firmly tell the receptionist that you will not be leaving until you’re seen the boss.
Sit in reception for as long as it takes to see the boss.
Hours, days, weeks, it doesn’t matter.
She can’t ignore if she sees you every day, all day.
If you really want something, sit outside her office.