Because the infinitive verb "ocuparse" means "to take care of." It may help to think of it as a different verb than ocupar.

Well spoted!

why did it present me with a word I have not learned "cuida' instead of accepting "ocupa"?

Maybe "Ella cuida la comida", but the "a" should not be used in this case (since it's only needed when the object is a person).

I don't think "cuidar" is the appropriate verb. "cuidar de" means "to take care of" in the sense of "tending to the needs of". For example...

"Yo no podía cuidar de mi hijo" = "I could not take care of my son".

"to take care of" has a broad meaning in English, so it could be translated by one of several Spanish verbs, depending on the context. It could mean she is in charge of organizing the food, or that she is cooking the food, or that she is making sure a hungry bear doesn't eat the food, ...

I agree that the multitude of uses of "se" are challenging to learn. Me,te,nos,les are a bit less confusing limiting the challenges to area 1 below. Here is a good summary of the uses of "se". It takes a lot of practicing and exposure to make this intuitive. I certainly need much practice in this area. If you know of more, please post.

http://spanish.about.com/od/pronouns/a/introduction_se.htm

1. Reflexive Pronoun a. To reflect the action back on the subject b. To indicate an emotional response c. To add emphasis d. To change the meaning or nuance of the verb http://www.spanishdict.com/topics/show/85
2. Passive voice
3. As substitute for le or les
4. Impersonal se

I read "Ella ocuparse de la comida" as "She to occupy herself with the food" or "She to take care herself of the food", which don't make sense in English, and I've confirmed with a native speaker that it's wrong in Spanish. Ocuparse is not the same as se ocupa (occupies herself), but se ocupar (to occupy herself).

Ocupar - to occupy. Ellos ocupan el edificio (They occupy the building). Yo ocupo, tú ocupas, él ocupa, etc.

Looking around, "cuidar" and "ocuparse de" are considered synonyms, so I'd think your answer should work.

However, synonyms usually have subtle differences. It'd be nice to hear comments from a native Spanish speaker.

You can use cuida de, but not cuida a. Prepositions don't translate exactly between languages, and I don't just mean English/Spanish! That said, in Spanish the correct preposition here is "de" not "a". It's often helpful to learn the verb with the appropriate preposition rather than trying to guess which one is used. The book "Spanish Pronouns and Prepositions" in the Practice Makes Perfect series has been helpful for me.

For various reasons: First, the verb has to match the subject. We have a third person singular here, so it has to be ocupa not ocupar, since the latter is the infinitive form (to take care). So what you wrote basically translates to she (to) take care of the food. Second, pronouns can only be attached to either the imperative form (e.g.: damelo - give it to me) or the infinive form (e.g. darlo - to give it). So while ocuparse isn't wrong per se, it's just not conjugated correctly. I don't know what your native language is, but I've experienced that many native English speakers find conjugating verbs quite confusing because in English all verbs have only one form for every tense. The only exception is the third-person-singular-s in the simple present. Most other languages - especially slavic and romance languages - require a specific ending which directly refers to the subject. I hope this doesn't confuse. Explaining grammar through the internet is extremely hard because I can't really tell how much you know about the language already. So ask away!

That's a challenge for me to comprehend too.

Ocuparse de is like saying "to occupy oneself with" so if someone takes care of the food, you could say they're occupying themselves with the task of providing / preparing the food for the event.

I've been speaking Spanish for a while now, and "tomar cuidado" seems so unatural. I'd be surprised if it were a valid translation for "take care".

The context of "take care of" in this sentence is "to assume responsibility for a task) so ocuparse de, as well as encargarse de, are appropriate options.

Whenever I hear cuidado on it's own it's in the context of "caution", or "be careful" so if indeed tomar cuidado is a valid expression in Spanish, it would be geared toward being careful rather than accepting responsibility for something

It's not really the same thing. Mom asked me to make dinner. Now she worries about the food being prepared....and might yell at me for not doing it.

I'm the one that is (or should be) actually taking care of it.

I think the "cerca" part. cerca means "near" It refers to close proximity. "Ella se hace cargo de la comida" is probably good. Although even better would be "Ella se encarga de la comida"

del is a contraction of "de el" there is no contraction for "de la"

That means "she takes the food away", which is different.

Not really. That means "blames himself/herself for".

Yes, it has. In Spanish we only join verbs with pronouns and never, under any circumstance with anything else.

For various reasons: First, the verb has to match the subject. We have a third person singular here, so it has to be ocupa not ocupar, since the latter is the infinitive form (to take care). So what you wrote basically translates to she (to) take care of the food. Second, pronouns can only be attached to either the imperative form (e.g.: damelo - give it to me) or the infinive form (e.g. darlo - to give it). So while ocuparse isn't wrong per se, it's just not conjugated correctly. I don't know what your native language is, but I've experienced that many native English speakers find conjugating verbs quite confusing because in English all verbs have only one form for every tense. The only exception is the third-person-singular-s in the simple present. Most other languages - especially slavic and romance languages - require a specific ending which directly refers to the subject. I hope this doesn't confuse. Explaining grammar through the internet is extremely hard because I can't really tell how much you know about the language already. So ask away!