I have had an experience with Helmi, as well. I took anglo concertina lessons from her in Burnsville at her home. I had her repair my father's concertina and she did a good job on that, as far as I can tell. She did a trade of an older English concertina (in moderate disrepair) for a new Defner (still can't find info on this concertina) that was a double reed concertina. A few keys stick, which is a bummer. I don't know if I got a fair deal, but I don't think it was a horrible trade.
As for her abilities, she did play a number of tunes for me in the course of the lessons and played them well, but all accordion type songs.
The lessons were a bit less thrilling, in that she literally gave me an accordion lesson book and taught in more of an accordion style. When I mentioned Irish music I got a bit of a brush off, almost like it was beneath her? I did understand that I was going into an accordion world with a concertina, and that was my own fault. But I have yet to find any other published concertina teachers in the Twin Cities, MN. (anyone?)
Overall not a bad experience but not a true concertina experience either, and not the greatest at that. And the following disclaimer: I'm a complete noob, I don't practice enough, and wouldn't know quality if it hit me in the face.
R