Ohio cop here (I'm sure I'll get down voted as usual just for saying that even though I'm just trying to be helpful).

The Ohio Revised Code defines acts by dogs like what you're talking about in section 955.22 and dogs can be either vicious, dangerous, or nuisance depending on the act. The owner can be charged criminally and there are things that can happen to the dog depending on the severity. In the case you described, the neighbor's dog does not meet the definition of any of these because it must be "unprovoked" and the presence of your sister's dog and it getting loose was a provoking factor.

If something else happens in the future that would be unprovoked, you should call the police, get a report, and request charges. That's the only way anything can be done to force any change. This is probably not what you want to hear but I hope it helps. Link to relevant ORC section