I have a different view here. Perhaps it might provide you with an entirely new perspective to look at the situation and consequently offer you more alternatives to deal with it. Instead of taking your side and agreeing with all your insinuations, let me try to play the Devil's Advocate here.
Understanding the Organization
First of all, let us understand that if you joined a company as an HR recently, where there was no HR or HR system earlier, it is safe to assume that it must be a private organization, likely a very small one. What is the present headcount? Since an HR has been recruited for the first time, it must be around 100.
Now, do you understand that in such a small organization, there must be face-to-face interaction between the staff? Everyone must know each other well, even to the extent of knowing their families. You have been here for three months as an HR. How well do you know your employees? Do you know what problems an employee may face commuting to work every day and then dealing with family responsibilities? A good HR's work is not restricted just to the workplace.
Sensitivity Towards Disabilities
The person for whom you used the term "handicap" has been working there for 7 years. Tell me, does a small private organization exist for charity to the disabled? By the way, it is very derogatory to use the term "handicap" for people with disabilities! Especially for an HR professional who deals with human beings, using a term like "handicap," that too with incorrect spelling; what can anyone infer about your capabilities and sensitivity? Are you not aware of what is the right term to use for persons with disabilities?
Moreover, you need to be more disability-sensitive and learn disability-language. As an HR with a long career ahead, you have a long way to go, and you will meet many "persons with disabilities" in your career in the future! So avoid becoming "emotionally-challenged"!
Performance Feedback
Despite complaining twice to the boss, nothing happened! On the contrary, you were given feedback on her good performance by the boss himself! What does it say about that person with disabilities? It only says that despite her physical disability, she is a star performer! You must be aware of how difficult it is to survive in the private sector if one doesn’t perform even for a few months, and this lady has been winning accolades for 7 long years. So, there is absolutely no doubt about her performance.
Understanding Misbehavior
Now, coming to the misbehavior aspect: What is "misbehavior"? And what is "being rude"? A person may not be soft-spoken or talkative. Another person may perceive this as being rude. A person may not, for whatever reason, greet you back when you say "Good Morning!" Some may construe it as misbehavior! Some may find it very offending—in the same manner, if you call a physically disabled person "handicap"! Just imagine if such persons are reading your post, what impressions they will have about you?
Conclusion and Suggestions
To conclude, I would suggest that you change your perception and attitude about people. Stop feeling threatened and try to accept people as they are. Not everybody can be sweet and nice to you, nor do they need to be. Acknowledge this fact and do not judge them based on what you think are their intentions.
Moreover, a good organization thrives on diversity. It is the hallmark of a thriving, growing company. It's good that your company believes in diversity at the workplace. It's good to know that your company is an equal opportunity employer in the true sense.
Finally, there doesn’t appear to be any instance of "bullying" because bullying is the use of force, threat, or coercion to abuse, intimidate, or aggressively dominate others. Two important aspects of bullying are: the person being bullied (victim) is weaker than the bully and the person is bullied to do something, which normally he would not do. In this case, both these vital elements are missing. So it might be construed as rude behavior or misbehavior, but it would need a really fertile imagination to call it a case of bullying, of a senior HR with no physical disabilities by a person with disabilities working as a receptionist.
Hope my words did not offend or hurt you because that was not my intention. If you are looking for a practical solution, then this is what I think might work: Go and talk to the employee concerned. Tell her how offended and hurt you felt due to her curt behavior with you, and how others also told you about a few such instances. In desperation, you went to the boss with complaints. And how the boss gave you feedback on her excellent performance and how happy he is to consider you as an asset for the organization.
Now, this suggested solution will only work if you shed your ego, hatred, and insensitivity towards others; and are able to convey your genuine feelings of appreciation.
Warm regards.