I would say nothing negative about it, only positive things. However; I would take an opportunity to show her some of my quilts. She would see the difference and make her own choice of how she would quilt her next item - stay with a little puff and loose stitches or go flatter with smaller stitches.

Please be kind and say nothing negative... no matter what you are thinking. Discovery is part of quilting. Let her discover her shortcomings for herself, and not point them out to her, lest you take from her the joy she had in creating the piece.

Unless she asks, "Why am I getting this puffy effect?", don't bring it up. Just encourage her.

Agree with the majority here.
Praise.
Think most of us new to quilting learn by observing others work. I can see where each item I've made could have been better. This is a learning process meant to be enjoyed.

I know your heart is in the right place, but I agree with Tartan that you shouldn't give advice unless it's solicited, especially since you don't know her well. She might be the sort of person who is very sensitive to critique of any kind, so she might take it wrong. Better to err on the side of silence, imo. :)

Words can be a very powerful thing to another person who is unsure or very critical of themselves, or if we as humans are having a bad day. So I have learned to choose my words wisely, before I open the door of criticism or positive. I try the positive first always.

NO, NO, NO!! What distinguishes the QP, and why we all hate them, is that they offer unsolicited opinions! If she says it turned out puffy and do you have any idea why, THEN you can offer your suggestion for improving it, but ONLY then. Even if she just says "what do you think", its still a better idea to just comment on the lovely fabric than give her technique instructions. Getting better in your quilting makes you more at risk for Quilt Police behavior, especially when you see someone who could really benefit from some free advise, but unless you are asked point blank, keep your improvement suggestions to yourself!

I'm agreeing with those, who say, "NO!" Unless she asks for advice and a lesson, don't offer criticism! Let her be proud of her efforts and let the buyer decide whether or not it's acceptable. Unsolicited "constructive criticism" often comes across as hurtful and snotty.

I have to go with the give approval where warrented group. Very nice thread indeed.LOL
However I also think it's great to offer availability for help in the future and the coffee visit. Having one of your runners where she sees it might offer the opportunity to say, "If you are wondering why I quilt my runners more tightly, it's because sometimes the things I sit on them tend to topple over if the runner is too puffy." Perhaps a bit more subtlity than I had there would be called for. :o

I would send the quilt police for doughnuts and only offer compliments. Being a newbie myself and getting "arrested" on my first project was very discouraging!

Quiltnmom and Neesie both said it! Be nice for a change. Being perfect can be very lonely. I would rather be remembered for being nice. So lets relax and enjoy the ride.