She has been reading since morning.

"has been" here helping verb.

If I have to put some adverb in "has been reading",Where should I put?

I mean

She has .

She has been .

Usually an adverb can be safely placed after the first verb of a verb phrase.
My suggestion is that the placement of adverbs, as suggested by CJ, represents the normal neutral placement. As he said, moving them often does create nuances, increases intensity and sometimes it changes the meaning dramatically.