Learn Russian: Она сорвала помидор с куста.

The preposition you use for 'from' depends on the preposition used for location. Because a tomato grows on a bush (на кусте), we must use its exact counterpart с (off of / from) to say where it came from. If it had been located inside something (using в), we would use из.

Does the prefix со- in сорвала have a specific meaning here?

Yes! The root verb is рвать (to tear or to pull). The prefix со- (a variation of с-) adds the meaning of taking something off or down from a surface. It is the perfective counterpart to the preposition с, working together in this sentence to mean 'plucked off'.

Why doesn't the ending of помидор change since it is the direct object being picked?

Because помидор is an inanimate masculine noun. For inanimate masculine nouns, the Accusative case (used for direct objects) is completely identical to the Nominative dictionary form. If it were a living thing, the ending would change.

What is the dictionary form of куста?

The dictionary form is куст (bush). Because it directly follows the preposition с meaning 'from' or 'off of', it must take the Genitive case, which means adding the -а ending for a masculine consonant-ending noun.