The widow of an employee who (1) has served 10 or more years and (2) withdraws before age 50, and (3) dies out of service before age 50, shall receive annuity, from the date of his death of the amount provided on a reversionary annuity basis from the following sums to his credit on the date of his death:
The annuity shall be computed as of the age of the widow at the date of the employee's death.
No part of city contributions shall be used to provide annuity for a widow in excess of that to which she would have had a right to receive if the employee had lived until age 50 and had not re-entered service and the annuity were then fixed for the widow on a reversionary annuity basis as of her age on the date when her husband would have attained age 50.
40 ILCS 5/6-136