In David Copperfield, why did Miss Betsey come to see David at school?

After Miss Betsey Trotwood decides to take charge of her grand-nephew David's education, she enrolls him at Doctor Strong’s school in Canterbury. She also decides he should be called Trotwood, as she had always wanted him named after her and thinks of David as his father. When they travel there together to accomplish this, she inspects several boarding houses and finds them all unsuitable; she and Mr. Wickfield, her lawyer, then arrange for him to stay at Wickfield’s house. During David’s first few weeks at school, Miss Trotwood travels to Canterbury several times to see him without warning, “with the view, I suppose, of taking me by surprise.” Apparently satisfied with his progress, both from her own observations and conferences with others, “she soon discontinued these visits.” Instead, David goes to Dover every three or four weeks and visits her there.
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