A runner from Stow is recovering just in time to hit the ground running. Caylie McMahon risked never walking again when she had a tumor removed from her spine. She plans to complete the Boston Marathon on Monday along with her best friend as part of the Spaulding Rehab Team. McMahon re-learned how to walk at Spaulding after her surgery. Now, she’s determined to give back to the place that gave her so much. “I was lucky my support system never on…