When she goes to Mexico, she will be visiting Chichen Itza.
When she goes to Mexico, she will visit Chichen Itza.
Is there a particular difference in meaning, or it is just the matter of style?
As other answers have indicated, the future progressive, as the term implies, can place emphasis on the ongoing nature of the future event. In such contexts the future simple is not correct:
This time tomorrow I'll be lying (*I'll lie) on the beach.
Sorry, I won't be able to make it. I'll be playing (*I'll play) tennis with Mike.
However, this is not the only use of the future progressive. It is often used when there is no particular focus on the ongoing nature of the future event:
You'll be hearing from my lawyer.
She'll be starting school soon, won't she?
In such cases, the future simple is also possible:
You'll hear from my lawyer.
She'll start school soon, won't she?
although, to my ears at least, these are very slightly less natural.
Now we come to the OP's examples, both of which are perfectly normal ways to tell someone of your friend's holiday plans.
There is possibly one small semantic difference, however. Namely, that the progressive form could carry with it the implication that the visit is part of an arrangement, whereas the future simple is a simple statement of fact. As such the future progressive parallels the use of the present progressive to express arranged future events:
I'm playing tennis with Mike tomorrow.
I'm visiting my grandparents at the weekend.
She's visiting Chichen Itza next week.
But in Fumblefinger's term, this is "armchair rationalisation", a process that no native speaker consciously goes through in advance of what they say in day-to-day conversation.
In summary, the OP's two sentences are virtually equivalent, but there are other contexts where only the future continuous is possible, or where it may sound a little more natural than the future simple.
Both the sentences have a similar meaning,but the first sentence emphasize on continuation of action.
*Basically, both tenses tell you that the action will happen in the future.
If you simply want to state that the action will happen in the future ? you can use the simple future. This tense gives no other data than the time --> Future.
The future progressive, however, tells you two things. 1) It tells you the time of the action --> Future 2) It tells you that the action will be IN PROGRESS.*
In conclusion, if you would like to say that the action will happen ? you can use the simple future tense.
If you would like to say that the action will happen, and you want to emphasize that it will be in progress at some time ? you can use the future progressive tense.
Please refer this link for detailed information..
To all intents and purposes, it's just a stylistic choice. I should also say that some speakers in some contexts might also just use Simple Present throughout...
When she goes to Mexico, she visits Chichen Itza.
...although it's worth noting that both this version and OP's second can also be used of habitual actions (i.e. - she often goes to Mexico, and whenever she does, she usually visits Chichen Itza).
Both sentences express an action in the future, and both meanings are virtually identical, however, there are some subtle differences.
When she goes to Mexico, she will be visiting Chichen Itza [taking photos, listening to the guides, climbing the pyramids, soaking up the atmosphere, etc.]
In this sentence I understand the tourist is going to visit Mexico and will spend some time touring the city of Chichen Itza. It implies the action will last a certain amount of time, perhaps a whole day or even a couple. The length of time is not specified, but the speaker's focus is on the action of visiting.
When she goes to Mexico, she will visit Chichen Itza [followed by an excursion to Park Ik Kil,.. etc.]
In this sentence the intention to visit to Chichen Itza may or may not take a day. The duration of the visit appears to be shorter than the previous statement. Again we do not know for certain but the impression is the city is included in the itinerary of Mexico but it is not the main focus.