Complex sentence: Starting around this time, Terrell started to have migraine headaches, but whilst it was not thought to be of significance at the time, family members would later state that these headaches may have been related to her later diagnosis of brain cancer.
Split into simpler sentences: Starting around this time, Terrell started to have migraine headaches. While it was not thought to be of significance at the time, family members would later state that these headaches might have been related to her later diagnosis of brain cancer.