I just bought a 3128 about a week ago. I haven't looked in the manual to see if there's a speed adjustment because for me, it's easy to adjust by not hitting the pedal so hard. There really doesn't seem to be an in-between speed, though. It's either very slow or away she goes.
I sew on a highly polished teak table. It doesn't run from me. She must be pushing it or leaning into it. That would be understandable since she's new to sewing machines.
I love my 3128. It's the perfect little straight line machine. And it's quiet.