I am sorry, but my answer is stereotyped:
- You are a male and the HR person is a female: accept
- You are a male and the HR person is a male: accept
- You are a female and the HR person is a female: accept
- You are a female and the HR person is a
male: decline -- heard too many bad stories about how guys manage relation in a office.
I see it as you have more gain than lost in this situation. Also, high rank people usually give good advice to advance your career. This opportunity can help you not only for the current process but all your next one.
One of my past experience was a female teacher invited me to a coffee shop. Her goal was to help me to get prepared for the final mandatory government language exam. I had already fail the language course once before.
So I went to grab a beer with her. She had brought my class exam that I failed, not the government. As @Stephan Branczyk mentionned, she had spotted gigantic mistakes that would make me fail the government exam. She gave me back my failed exam, explained some strategies and instructed me to play it safe on the exam. Then she told me to do again the same class exam at home and give it back to her. I did it again and I got a very good grade that make me pass the course and also I succeed the government exam. She told me that she gave the opportunities to 5 others students. All of them agreed to redo the class exam at home but only me and another one have invested the time, so the 4 others failed.
Another person told me a similar story (female-female) where she declined the offer of the teacher because this troubled her values. There is a rule where you cannot take a class after you failed 3 times. So you cannot graduate because you did not complete all required courses. I admired her honesty but this impacted considerably her life without a diploma. She could invested another 3 years to study for another diploma but she did not have the strength/motivation after the failure.
Life is filled with opportunities and you are your own judge of your actions.