What's the difference?

[Hobbit]

Ella se mira al espejo.
Ella se mira en el espejo.

Ella va a la tienda.
Ella se va a la tienda.

Ella entra en la oficina.
Ella entra a la oficina.

Ella pone la botella sobre la mesa.
Ella pone la botella en la mesa.

[AngelicaDeAlquezar]

The differences are, I think in regional and colloquial usage:

Ella se mira al espejo.
Ella se mira en el espejo.
Both have the same meaning. Some speakers would find "al espejo" more educated, but I think it's just a matter of regional preferences.

Ella entra en la oficina.
Ella entra a la oficina.
Both have the same meaning, and the same case as the first pair of sentences. Probably some speakers will find "a la oficina" more appropriate.

Ella pone la botella sobre la mesa.
Ella pone la botella en la mesa.
Same meaning and previous cases. Some speakers believe that the use of "sobre" could be more explicit and thus more appropriate.


Ella va a la tienda.
Ella se va a la tienda.
The pronominal particle adds emphasis on the fact that the person is leaving for the store, while the first sentence makes a neutral statement about her going to the store.