Quoting TantricLemons:" I can totally understand that. Will she let you mess with her. Because you can measure and mark where ... [snip!] ... fit on her waist. I would go in and ask them what to mark and where. Let them show you and just do it yourself and bring it in."
Quoting £egendary Zeppelin:" I always have to take my kid when shopping for pants. They just all fit so different "