TOPIC: "I'm with XXXX company now" OR "I work for XX

Today I learnt the following sentence.
Kathleen is with the National Institute of Mental Health.
I thinks it's the same as "Kathleen work for the National Insitute of Mental Health.
According to this,
I can use
"I'm with XXX company now" to replace"I work for XXX company".
Could you please tell me if I 'm correct?

Thanks

About the sentence which you just learned:
"Kathleen is with the National Institute of Mental HEalth."
You're wondering if it's the same meaning as " kathleen WORKS for the National Institute of Mental Health" , and if so, if you can use " I 'm with XXX company now" to replace "I work for XXX Company".