You ask the maid to write the actual resignation date. You write a letter accepting the resignation and allowing her to leave immediately. Plus, you can waive the balance of payment-in-lieu after deducted her AL and food & travelling allowance. Then, you ask her signing on the letter.
I believe you don't want to waive her 1 month payment-in-lieu, but still pay her AL and food & travelling allowance.
Before accepting her resignation, please check all your valuable / non-valuable belongings and your kids' health. Some maids leave suddenly because they stole valuable things or hurt the kids.