i have a lady who cannot roll like a ball. .how can i help her.what will help mobilize that thoracic spine?

Hi Susannah -- I also have a "flat" spine which makes articulating my lumbar and thoracic very challenging, especially during roll downs. If your client has a strong core and is well versed in proper ab engagement, it may be as simple as telling her to focus on "pushing" her lumbar into the mat first. From the start position, it almost feels like I go into a slight 'imprint" (even though I'm already in flexion) which helps me to "isolate" and feel my lumbar connecting with the mat. For some tactile help, you can place your hand on her lumbar and ask her to push your hand away before rolling or put her up against an arc barrel/spine corrector first and have her push her lumbar into the barrel with table top legs. As she loses the lumbar contact, she can figure out how to engage in order to connect again. That way, she can feel the sensation of leading with the lumbar spine.
Hope that made sense to you. Good luck!