In a sense she comes off more like an adopted elder sister that has to fill a motherly role, rather than an actual stepmother, not all that different from how the eldest sibling can sometimes take on a motherly/fatherly role to the younger siblings.
In either case I like stories like this where characters accept each other as family despite no blood ties, good-natured stepmothers tend to be a breath of fresh air due to typical the evil-stepmother trope.