Child abuse is no small matter, and yes, shoving a child against a wall could be considered abusive under some circumstances, and charges might be filed if warranted. However, you need to understand that reporting a family member for child abuse without substantiated proof and a true need to protect the child could destroy their family. Child protective services is indiscriminate and heavy handed, and the result could be unexpected, e.g. the children could be taken away entirely, from all of your family members.
If it is a growing concern for your family, I would suggest that you speak with Suzy about her temper and see if she will get counseling for her temper. Additionally, your family should consider not having Suzy babysit anymore. Have you spoken with Heather's parents about any of this? What is their opinion? I would respect their wishes if they are dealing with the situation themselves.
There are better ways of approaching this problem than endangering your family by involving the state. Work with your family and solve your issues together.
Attorney answers to questions are for general purposes only and do not establish an attorney-client relationship. This answer is meant for informational purposes only and should not be construed as legal advice within the bounds of a professional relationship. It is always best to seek counsel with a competent attorney experienced in your area of issue and fully informed about the facts of your case.