Since......ago

Today my friend posted a post. She wrote: I have known her since ten years ago. We clicked immediately. She meant 自从十年前我认识她..... Other friend said: the first sentence is not correct. 'since' and 'ago' can't be used together.

I have known her for ten years. (use "for" with duration -- for five minutes; for two months)

I have known her since 2009.  
use 'since' with specific time in the past; since yesterday, since last month + present perfect.
I have been watching tv since 7 p.m.
He's lived in Japan since 2012.

I met her ten years ago. ('ago' shows past, and is used with a past tense: five minutes ago; a month ago)

Since......ago

Today my friend posted a post. She wrote: I have known her since ten years ago. We clicked immediately. She meant 自从十年前我认识她..... Other friend said: the first sentence is not correct. 'since' and 'ago' can't be used together.

In conversation you will hear 'since' and 'ago' used together all the time.

Exactly the same as your example, for instance: "I have known her since 10 years ago'

There is nothing wrong with this statement.