step-parents spanking

I am a single mom of 3 children. My daughter is 7 yrs old, almost 8.. Her
bio-father just decided he wants to play daddy after being the absent
parent for 7 yrs, he's been getting his visitations with my daughter
every
other weekend.
Now I have a real problem with my daughters bio-fathers wife spanking my
daughter. Recently the step-mom spanked my daughter because she wouldn't
put her pajamas on, well if you knew my daughter you would definetly say
she doesn't deserve to be spanked, sometimes she can be hard to handle
with her adhd, but that doesn't give the step-mom any rights to spank my
child or to land a hand on my children. I have no problem with the
discpline but physical discpline is so dead on wrong.
So what are your thoughts on step-parents SPANKING your child/children?