Gross and habitual neglect of duty; proportionality of penalty for absenteeism practice question

ABC Garments Corporation employed Linda as a regular worker in its Finishing Section for six years. Over a six-month period, Linda was absent without official leave on four occasions: for the first three, she was successively given a written warning, a three-day suspension, and a six-day suspension. On the fourth absence, she claimed illness and said she submitted a medical certificate, but the company denied receiving it. Upon her return, ABC Garments dismissed her for habitual absenteeism, citing company rules. Linda filed a complaint for illegal dismissal. Should Linda's dismissal be upheld as valid? Explain.