What's the difference between 心配しないで and 心配しなくても?

心配しないで means "don't worry!".
心配しなくても means "It's nothing to worry about!".

I think they both mean the same.
But someone told me that the nuance is slightly difference in Japanese.

Can you enlighten me about the nuance, when to use 心配しないで and when to use 心配しなくても? I still don't get it.
Okay, the situation is this girl is talking with her (male) best friend. She's sharing her worries about almost turning 30 and not married yet. Then her best friend told her "心配しなくても".
What's the difference with saying 心配しないで?

Question

What's the difference between 心配しないで and 心配しなくても?

心配しないで means "don't worry!". 
心配しなくても means "It's nothing to worry about!".

I think they both mean the same.
But someone told me that the nuance is slightly difference in Japanese.

Can you enlighten me about the nuance, when to use 心配しないで and when to use 心配しなくても? I still don't get it.
Okay, the situation is this girl is talking with her (male) best friend. She's sharing her worries about almost turning 30 and not married yet. Then her best friend told her "心配しなくても".
What's the difference with saying 心配しないで?

Answer

Yes, it's kind of same. 心配しないで can be used as a phrase, like you say " Don't worry"
心配しなくても needs add some sentences and it can't be used on it's own.

Example:

心配しなくてもいいよ。
You don't need to worry about it.

心配しなくても来るよ。
No need to worry, he/she/somebody will come.

However you can use 心配しないで+ sentences but it sounds like casual.

Example/same meaning 
心配しないでいいよ。
心配しないでも来るよ。

Just in my opinion and feelings 😌

Answer

心配しないで Don’t worry!
心配しなくても Don’t have to worry!

Answer

「心配しなくても」は後ろに言葉が続かないと、少し変な感じがします。たとえば「心配しなくてもいいよ」とか「心配しなくても大丈夫だよ」だと自然な感じになります。
You gave me the sample story of no-merriged women. If I were her ,I said "心配しなくてもいいんじゃない?".

これは私の意見ですが、言葉も大事ですが声のトーン(tone )や表情もメッセージを伝える大事な要素(factors)だと思います。