Learn Croatian: Ona radi s kolegicom. - She works with a colleague.

The preposition meaning "with" is usually just s. We only add the "a" to make it sa when the following word starts with a hissing sound (like s, z, š, or ž) or certain consonant clusters, making it hard to pronounce. Since kolegicom starts with a "k", the short s is perfectly fine.

Why does the word for colleague end in -om in this sentence?

The preposition s (when used to mean "in the company of") requires the following noun to be in the instrumental case. The dictionary form of this word is kolegica (female colleague). For feminine nouns ending in -a, we drop the -a and add -om to form the instrumental case.

Does kolegicom specifically mean she is working with a female colleague?

Yes! The base word is kolegica, which refers to a woman. If she were working with a male colleague, the base word is kolega. Even though kolega is masculine, it ends in -a and changes endings like a feminine word, so "with a male colleague" would be s kolegom.

How do I pronounce s kolegicom? Is there a pause after the s?

There is no pause. Even though they are written as two separate words, you pronounce the preposition s as if it is attached directly to the front of the noun, sounding like one continuous word.