she's talking about or talked about

I walked to the nurse desk and asked for a bottled water and one of the nurses told me that I couldn't take any liquid before surgery. Instead, she told me to get some rest. I walked back to my room and told my mom. Mom said, "Sounds like she knows what she['s talking about/talked about]." Which is correct and why?

Thanks in advance!

I have no problem with the past tense because clearly it was something in the past.

With the present tense, it sounds like the nurse is telling/has just told the person in front of his/her mother when she makes the comment.

Mom said, "Sounds like she knows what she's talking about."

'She knows what she is talking about' means 'She knows what you have to do.' It doesn't imply that your mother was near the nurse when she told you what you should do.

New2grammar

Let's say X tell you something and when you get home, you tell your sister, "Mr.X told me about or tells me about", which is correct?

I would choose the past tense. The same reasoning for my original.

Then your sister might say - "sounds like Mr X knows what he is talking about! 

Maybe the purpose of my second example isn't clear. I was just trying to emphasize the fact that the conversation took place in the past. So when referring to the past exchanges, we should use the past tense. Similarly, the act of the nurse telling the patient was in the past so when one refers to the act, logically, the past tense should be used like "My dog bit me" and not" My dog is biting me". I'm not sure if my explanation makes any sense to you. The focus is the timeline.