Presumably, you are asking why "...to see her PLAY her song" instead of "... to see her PLAYING her song."
"...to see her PLAY her song" means to see her play the whole song: beginning, middle, and ending.
"...to see her PLAYING her song" means to see her playing (after she has started).
Practical English Usage 3rd edition by Swan, section 242.
Hear, see, watch, notice and simlar verbs of perception can be followed by object + infinitive (without to) or object + -ing form.
I heard him go down the stairs.
I heard him going down the stairs.
There is often a difference of meaning. After these verbs, an infinitive suggests that we hear or see the whole of an action or event; an -ing form suggests we hear or see something in progress, going on. Compare:
- I saw her cross the road. (= I saw her cross it from one side to the other)
- I saw her crossing the road. (= I saw her in the middle, on her way across)
If you are asking about "We NEED ..." and "We are NEEDING," the verb "need" is normally used statively in Britain and North America.
However, "stative" verbs often have multiple meanings, static and dynamic. Here is an excellent explanation by Su.Ki.
Also, stative (non-progressive) verbs sometimes take a progressive form.
Practical English Usage 3rd edition by Swan, section 471-3.
"Occasionally 'non-progressive' verbs are used in progressive forms
in order to emphasise the idea of change or development.
These days, more and more people prefer / are preferring to take early retirement."