I am a longerarmer and I am very disaapointted in her statement to you.
Tension issues are unaccepptable. It can be fixed with the first bobbin test .
I use all kinds of thread,varigated,thick,thin,mettllic,etc and never had tension troubles.
She should have ripped it out and re did then or give you a huge discount.
I'm ripping out a corner of a quilt,not because of tension trouble,the thread I choose disappears in the fabric and I can't see it. If I'm unhappy I know the owner will be unhappy. That's my rule.
Hope you can resolve this.
here is a picture of my dble wedding ring I did for a cust. She wanted 3 layers of batting and this is a King quilt.