Workplace Issue

I have an issue and want to handle it properly. I have a co-worker who is my assistant but I am not this person's supervisor. This person has done some things that makes trust difficult, but per my boss this person needs to know everything I know because my position in the company is critical and a competent fall back position is vital.

The problem is that the person tries to get me to do things the way that think it needs to be done even when lacking knowledge of the task or area of concern. Never confrontational, disrespectful but persistent. Unlike most workers who are content to do a good job and go home. This person at times wants to do my job and do it their way, which is not always possible or practical. This person likes to take chances and short cuts, something that has serious consequences since everything they work with is my responsibility. Often this person tries to force me into making decisions by using this phrase "Do you want me to do . . . .?"
Which I see as an attempt to corner me into allowing certain actions that I otherwise would do myself, or have not even considered. If I say yes, then they get their way, and if I say no, I can be perceived as the bad person, with-holding tasks because I fear that this person will outshine me. At times I do allow the action, but it gets to be aggravating to get this all of the time.

One of my co-workers says that the company is getting a manager for free, which is correct to a degree, but I have tried very hard to direct this person to our common boss as much as possible. But that is another story.

I try to be fair and balanced with my own responsibilities and would never deliberately mistreat this person, but at times it can be unnerving. I want this person to succeed, but not at the expense of my job or peace of mind.

ny_sane

Hi, ny_sane! Could you explain the situation to your boss or someone who deals with these issues professionally? Maybe your assistant needs to hear some of this stuff even if it's just in a gentle way.
You could take the chance of seeming like "the bad guy" and explain in a calm tone of voice that you appreciate their dedication, but that this or that is part of your job, which you've been doing for a long time, and you'll do it yourself and in your own way. You could explain why your way of doing things is best too.
I think you need to stand up to him/her a few times and if things get weird, you can always tell your boss and explain why your way of doing things is better and that you have more experience too.