In ch.6, Mrs. Musgrove tells Anne why she has a poor opinion of Mary's nursery-maid: "she is always upon the gad; and from my own knowledge, I can declare, she is such a fine-dressing lady, that she is enough to ruin any servants she comes near".
She likes to be out and about and she dresses too well! Of course, no employer would want her wandering off when she was supposed to be taking care of her charges, but really, I have a sneaking sympathy for the nursery-maid. Imagine wanting a bit of interest and excitement in your life when you could be keeping your nose to the grindstone 24/7! Also, what if all the servants started dressing so fine - you might not be able to distinguish them from their employers!