It is perfectly grammatical to say and write:
She finds for herself what she should study.
but many native speakers would not say it that way and would be content to place for herself or herself at the end of the sentence, trusting to their intonation to indicate that for herself or herself reflexively modifies finds.
She finds what she should study, herself.
Another way to say and write it would be:
What she should study she finds for herself.
If your meaning is that she pursues her own interests or follows her own desire, then should might not be the best word, and you might want to replace finds with decides:
She decides for herself what to study.
What to study she decides for herself.
You can keep should if you want to stress the idea that she herself is the judge of what would be prudent for her to study:
What she should study she decides for herself.
She decides for herself what she should study.
Modal should conveys the idea that something would be prudent or advisable.