I'm not sure if you saw my questions. I asked them because they have legal significance.
In employment law, if you do not have an employment contract stating that you can only be terminated for cause, your employment is "at will." This is important in understanding the protections your job has. At will employees can legally be terminated at any time. This also means that they have no legal right to their job, so generalized harassment is not illegal for them. This comes from the Supreme Court of the United States.
So, then the issue becomes one of understand exactly what the basis for the harassment you've been facing is. For you to be able to claim any sort of illegal act by the employer, you would have to allege that there in an illegal motivation for the harassment. Among those illegal motivations is discrimination based on race, religion, gender, age, disability or recent medical leave. Now, you mentioned the age disparity between yourself and this other person. That alone is not enough to make a claim, though it certainly is a start. If you could show that you are the only person treated that way (and the only person who is older), or that she only treats older employees that way, or that she has made negative comments concerning age...that would all be additional evidence to support a claim of discrimination, which you should make to the Equal Employment Opportunity Commission in your state.
If you can't allege any form of discrimination though, your entire recourse is based on what HR chooses to do here and if they choose to do nothing, that's not illegal unless you can point to a strict company policy making any form of harassment illegal. Then you could sue the company based on breach of their implied contract (the policy).
Finally, to address the boss being the daughter of an administrator, nepotism is not illegal in the U.S., so this fact doesn't really help you.