Depends on which is more important- the quilt coming out the way you think it should, or your relationship with them and their feelings.
If it was my sister, I'd tell her, "This is incredible, I can't believe you're already this good! With this batting, I'd quilt closer together though, because it has the tendency not to stay together... double check the bag, too, because different battings have different amount of inches you can have your quilting spaces. Sometimes, they'll get all warped in the wash if you don't do it close enough together... and I'm not criticizing, I LOVE what you did!"
My sister and I are close, and I'd never want to hurt her. I don't care if people are thick skinned or thin skinned, or whether they SHOULD be or not, I tippy toe because I hate hurting people in my life. Also, I don't think there's a wrong way to make a quilt as long as the creator is happy with the outcome. If they don't want it to last forever, I'm not gonna tell them they're wrong.

I would just make sure they know that when quilting there just be stitches at least every one inch. Other then that I guess we all learn from our mistakes.

That's a tough one. But in my husbands family a phrase "it has enough" would mean "let it go for better or worse".

I know how you feel. A quilt is a terrible thing to loose.

Also, the first line of what I posted looks catty and that's not at all what I was going for. I'm sorry it came out like that!

I would admire and highly praise the work they have done. I would not say anything about the lack of quilting and let them find out for themselves if the amount of quilting they have done is adequate. Some times the best lesson learned is the one we learn for ourselves.

Totally agree, this is one battle you should not attend.
We all have to learn from our mistakes.

Thinking back to when I first learned to sew... to be honest, I was not interested in cutting the pattern "thread perfect" as our teacher wanted. All I was going for was a finished product. The 1st quilt I made... I was just making. Now I shoot for things/patterns a bit more complicated. It's a learning process and your girls will learn. In the mean time, you've taught them another skill.

I don't know that I would say anything unless asked. When the quilts are washed and have issues then you might ask about the batting and offer suggestions at that point. Compliment them on a job well done. If you had worked with them on a routine basis you could have offered suggestions at that point. Now saying anything will be critical of them.

Good luck.

I wouldn't. She may get discouraged and give it up. She will learn as she goes.

I agree with this.