I'm fairly new to quilting for others and I agree on a written estimate for both to sign, measure the quilt with her and get out your calculator and give her the number out loud, ALSO measure her backing while she's there. I know sometimes it's hard to hold our tongues. Try to take a deep breath and think about what you're about to say and hopefully use the correct tone to be professional but not let people talk down to you. good luck in the future