HELP - Employee has to be reminded what to do daily. What to do?

I've been in my office manager role for about a year. I've trained one other person who ended up doing very good with the company, she was thorough, precise. Exactly how I trained her to be and more. She left about 3 months ago and we've gotten a new employee since.

The new employee started at the end of January. She's come up to speed pretty well. My boss who is above me is happy with her performance, although we have both noticed somethings. She doesn't remember things accurately or fully, She doesn't read through full emails, missing important details in the emails that is pertinent. She's told customers the wrong things. I constantly have to remind her to do a task that I've already told her to do. During training I noticed that she wasn't asking any questions and I've noticed that still.

I've spoken with my boss about my observations. When I notice something is not being done correctly, I usually correct her right then and there so there's no confusion. However, these same mistakes keep popping up. I've told her multiple times to come to me with any questions she may have as the industry we work for is very niche. Her not doing this has resulted in wrong prices being told to the customers (not like $10-$20 off, but thousands off). This has resulted in loss of sales and a poor image on the company. I've asked her if she needs any help and she never says that she does and when I correct her on the mistakes she's made she just says okay.

She was hired to help me with work that I do, but I feel right now I'm having even more work because now I'm constantly checking over things to make sure no details were missed, orders were submitted correctly, the correct prices were given. I've spoken to my boss about making sure to document when I'm reminding her off stuff and other things.

How do I help her? I want to be a good manager, I want to also have her do the work correctly and efficiently. I feel as though I have very good communication, my boss loves that about me and why he chose me to be the office manager.

Any advice is appreciated!! :)