You have an exempt employee who is officially at 20 hours a week. Because she is exempt she is paid the same amount every week, regardless of how many hours she puts in. She frequently works more than 20 hours, but no time cards exist.
She has a baby and requests FMLA. On her official schedule of 20 hours a week, she has not worked the requisite number of hours to qualify under the statute. She claims with the additional hours she has put in, she more than qualifies. Her manager agrees. (FYI, I believe you need 1250 hours in a year for FMLA to qualify. Assume her company meets the other qualifications for FMLA and she has been there more than a year.)