I'm the odd one out but if I were her, I would try and return them as defective. Knowing how much spandex or other stretch material is in jeans isn't going to tell you how good or bad the item will wear. The only way to tell is to wear them. I have jeans with 3% spandex in them have slid down like a bad pair of pantyhose all day. They drove me crazy and were unwearable. I own flexibelle jeans that have 8% spandex and have no problem with them stretching out or sliding down.
I used to shop at Dillards and yes they are more strict with their return policy but there are exceptions to it. IMO she needs to go into the store, not call on the phone. It's easier for someone to be told no over the phone than it is to her face. Dillards stores have different managers so whether this manager will consider the jeans defective or not, who knows.
If she wore them all day, that is different.
I bought a pair of shoes and stupid me, wore them to a wedding Friday night. I never wore them around my house first. They are the most miserable shoes I have ever owned. They are so uncomfortable, I could barely walk within 30 minutes of having the shoes on. They are a peep toe and the opening of the toe part dug into my big toe and literally cut my toe. And the fit on them was fine. They were not too tight or small in any way. It's just the way the shoe is made. The reviews on the shoes are really good. Even if they hadn't cut me, they were just uncomfortable. Lesson learned.