[Grammar] That's so cute of you!

[Rollercoaster1]

I watched a video in which a little girl was describing what interjections are, while her mother was there in the video.
Will it be right If I comment "That's so cute of her describing interjections."?

 

[emsr2d2]

I watched a video in which a little girl was describing what interjections are. [STRIKE]while[/STRIKE] Her mother was [STRIKE]there[/STRIKE] also in the video.

Will it be right if I comment "That's so cute of her describing interjections (no full stop here)"?

Not really, no. You could say:

That's a very cute video of her describing interjections.
That's so cute! She's describing interjections.

Why is it relevant that her mother was also in the video?

 

[Rollercoaster1]

Not really, no. You could say:

That's a very cute video of her describing interjections.
That's so cute! She's describing interjections.

Why is it relevant that her mother was also in the video?

The video was sent by the child's mother who's an English teacher. I was commenting on the child describing interjections while addressing her mother.

 

[emsr2d2]

In that case, it would have been better to say "I have seen a video in which a little girl explains interjections to her mother."

 

[Rollercoaster1]

In that case, it would have been better to say "I have seen a video in which a little girl explains interjections to her mother."

Her mother is an English Teacher. She often sends me emails and video links regarding English language. The video I discussed about here was sent by her mother to which I replied and commented on her daughter.

In your explanation above in this post, it suggests that Her mother is an anonymous to me. It also means that I am telling someone else instead of telling her mother.

 

[emsr2d2]

There is absolutely nothing in your first post to suggest you know the mother or the child personally, nor that you are talking to the mother. In addition, the sentence in your title "That's so cute of you!" does not appear anywhere in your post.
As Piscean said, we need context and relevant information in post #1. Here is how I would have written your post:


Title: That's so cute of her describing interjections!

I have an acquaintance who is an English teacher. She often sends me links to videos in which her daughter explains aspects of the English language. She recently sent me one in which her daughter was describing interjections.
Would it be correct if I commented "That's so cute of her describing interjections"?

If you're commenting directly to the mother (or perhaps writing a comment under the video), stick with "That's so cute!"