First off, ask yourself if you really want to make this quilt and if you have time. Choose a sample project and create a one sheet that shows average material cost, average time spent making a quilt, and break down what one would normally charge for a handmade item. I'm not sure if you're planning to charge her, but even if you don't this will be helpful for her to be able to conceptualize the amount that goes into making a quilt, most people really don't know and feelings can get hurt or pressure put on just because of a lack of clear communication.
Secondly, ask HER what her expectations are in the following areas:
1. Time frame - does she want/need it by a certain date and by extension are you willing and able to complete it by that date? This is the most important thing to clarify with her and I think the thing that could cause the most pressure and frustration on your part. There's nothing worse that being under the gun on a project you have no desire (or incentive) to work on. If she's not going to pay you beyond materials (see below) than make sure she understands that you will work on this when you want and there is no due date.
2. Design - tell her you require her to be involved in the design process, especially if she is paying for the quilt. Ask her what room it's for, what colors are her decor in that room, have her look on pinterest and show you some ideas of what she likes (modern, traditional, etc), and find out how big she needs the quilt. Once you have a basic design, present it to her, along with budget for materials costs, labor costs, and a completion date that won't put you under a deadline you can't handle.
3. Cost - this is both cost of materials and opportunity cost. Remember economics 101? Opportunity cost is equal to the stuff you'll be missing out on if you invest your time in this project. Be clear with her about how much time you think it will take you. If she is not paying you, set the expectation that it will be done on your terms and not hers and it can take years to complete a quilt. Also, tell her you require payment in advance and if she approves the design payment is not dependant on whether she likes the final product or not. You can't custom order something and then change your mind without suffering some kind of loss.