How do I prove that someone is negligent?

This question applies to a Montgomery County, MD resident. An 82 year old woman became intimidated by a barking dog that ran out of its apartment and was approaching her. In an effort to try and escape, she fell and suffered a broken pelvis. The incident occurred in the public hallway of the apartment where the woman resides. There were no eye witnesses to the fall. The owner came out shortly afterwards after hearing the dog barking and found the woman lying in the hallway.The dog's owner was sent an email by the victim's daughter on her behalf telling him that he would be mailed the bills for medical services. The dog's owner replied via email that he is shocked and appalled at this and is not responsible for any medical bills, but later followed up with another email where he gave her an email address to sent the bills to. After the bills were sent, he responded again saying he is not responsible and won't be paying. It does not make sense to want to see bills if he is claiming he is not responsible. Could this be used against him in a lawsuit, since there are no eye witnesses? Thanks for your response.