Hi! I'm not saying the translation is wrong, I'm just saying that in Spanish, we sometimes are a little more "verbose" when talking. For example, I would have translated that phrase to:
"Ella trabaja en una empresa muy grande que se dedica a (la) ingeniería."
The thing is that English has this way of expressing ideas by just jutting words together (something I happen to like a lot about the English language), but sometimes it doesn't work too well if you try to do the same in Spanish (or other languages, for that matter). In this case, it works, but if you want to emphasize that "big" refers to the company, you are right, you should put "gran" or "grande" before or after the word "empresa".
The last thing I want to add is that one possible reason for that translation is that we don't usually use the adjective "grande" or "gran" with "ingeniería". When we use "ingeniería" we can use the words "excelente", "de alto nivel", "avanzada", etc.
Now, when you talk about an "engineer", you do hear frequently "es un gran ingeniero", but in this context, it means "he (or she) is a great engineer", in other words, he's good at his job, not that he is big in size.