I'd be happy to assist you in finding the email response from your customer, Kathryn.
When you send estimates to your customers, they can reply directly to the email. Their response will then be sent to the Customer-facing email associated with your sales forms. Please refer to the screenshot below for reference:
You can modify and find their response in that specific email. If it's not there, please check your spam or junk folder. If it still isn't there, ask your customer to resend the reply and check again.