Thats strange, the light is reflecting on that spot so I can't tell but was there any cut or scab there? If she nicked her and got skin I'd assume there would be a scab after. How long ago was she groomed and did you notice right away after or few days later?
I don't think it may of been the groomers because I would just think if it was there would be a scab or something. But then again I am not a professional so what do I know