"in ihr Haus" is accusative - when something is physically moving into, over, through something else, the phrase is accusative. e.g. "Er schwimmt ins Wasser."
When something is stationary with the same prepositions e.g. "Er ist im Wasser." it is dative.
This is just like the classic example with Switzerland "Ich wohne in der Schweiz" versus "Ich reise in die Schweiz"
The difference in meaning between going to her house and going into her house is that, in the first example, she could be strolling up the walk toward the door or, perhaps, just leaving the airport across the city. In the second example (going into her house), she is actually crossing the threshold.