Invisalign Retainer Very Tight and Difficult to Remove?

2.5 years of wearing braces, the DDS. crafted an invisalign "retainer". This appliance is so tight, and It is incredibly difficult to remove. In fact, I observed my daughter using two hands and a great amount of force to remove the appliance to brush her teeth, and this was not enough for the retainer to come out. She tried several times to extract the thing. When it finally released its hold on her teeth, it made her bleed. I need to know if this is normal or if the appliance was made wrong.