"I need that bear for her."
Translation:Toho medvěda potřebuju pro ni.
Yes, it is the same preposition in English , and English needs the preposition in both cases.
On the Czech side, hledat does not need to be followed be a preposition, only by a noun in the accusative case. But the construction "for her" in this sentence does require the use of a preposition, because potřebovat behaves dufferently.
These are things that, over time, will lodge themselves in your brain. But we all learn at a different pace, and there can be plenty of frustration involved in reconciling Czech and English!
I suggest to return to the first two skills and review the Tips and notes about Czech orthography and pronunciation. The letter I makes DI TI and NI to be pronounced as ĎI ŤI and ŇI. There is more to be reviewed. For example, the effect the letter Ě has in similar groups.