Your question suggests that Jane had a clear idea of what she was expecting when she was sent to Lowood. Actually, the text indicates she had no such idea and that she went to Lowood without any thought of what it might actually be like. I suppose one aspect that would have surprised her was the poor quality of the food and its lack in terms of quantity. Consider the description of the porridge at Jane's first breakfast:
Ravenous, and now very faint, I devoured a spoonful or two of my portion without thinking of its taste; but the first edge of hunger blunted, I perceived I had got in hand a nauseous mess; burnt porridge is almost as bad as rotten potatoes; famine itself soon sickens over it. The spoons were moved slowly: I saw each girl taste her food and try to swallow it; but in most cases the effort was soon relinquished. Breakfast was over, and none had breakfasted.
This poor quality of food is something that Jane has to become accustomed to, as want is something that defines her early years at Lowood until after the many deaths that we caused there. This would be one aspect that she would not have anticipated. I also think she may not have anticipated forming such good friends and relationships there with Helen Burns and Miss Temple.