Can I create a Scheduled Order for a customer who forgot to choose Autoship at checkout?
Yes! You can create a new scheduled order for your customer as described in this help doc: https://support.autoship.cloud/article/400-scheduled-orders
Note: if the customer did not choose to save her payment method at checkout (which is only required when a product is scheduled for Autoship at checkout, but optional otherwise), you may need to add her payment method to her Scheduled Order a different way.
If this is the case, you can request that the customer add a payment method via My Account > Payment Methods and then add it to their Scheduled Order in My Account > Scheduled Orders or you can add it to their Scheduled Order for them after they've added it.