I am so sorry about what to your little Dolly. this is so wrong on some many levels!
If I were you i would be , first taking pictures of the injury, the I'd be folling up in a small claims court ! I think what they did is highly unethical and handeled in the most unprofessionl, terrible way ! They can't just do that to your baby, without calling you ! What they said to you was to try to cover their own assess... YES, it is a big deal, and They were wrong for hurting Dolly in the first place, then over stepping their boundaries by giving her the medical treatment without your knowlege. that was done on purpose so you would not know how bad the wound was. Of course it was serious enough for stitches, right? Sayinf that she did not need them, was only to cover their own butts for what the groomer had done. That is so wrong ! That groomer hurting your Yorkie so badly she needed stitches? That is unthinkable .I'd be out for blood if it were my Suzi.