Wa-bayḍati is genitive even though the later verb tamattaʿtu is a first-person perfect. The construction is commonly explained by an understood rubba after the wāw: wa-rubba bayḍati khidrin, “and many a / such a sheltered woman.”
Bayḍati is genitive and acts as the first member of an iḍāfah; khidrin is its genitive complement. Tamattaʿtu then narrates what the speaker says happened. Simply treating the wāw as ordinary coordination would not explain the initial genitive form fully.
PartFunction
Wa-Wāw conveying an understood rubba
BayḍatiGenitive after implied rubba; first term of construct
KhidrinGenitive second term of construct