Aunt Alexandra is motherly to Scout in ways that Scout doesn't necessarily appreciate:
1. Alexandra likes to declare what's best for the family. Therefore, she often tells Scout about what Scout should do. This includes having an intentional focus on the heritage of the family. She wants Scout to read her cousin's book, and to meet her cousin Lily. Neither of these really impress Scout.
2. Alexandra tries to lead Scout by example. She doesn't really like that Scout happens to be a tomboy, so in addition to wearing appropriate Southern belle clothing, Alexandra encouraging sitting, cooking, and needlework as appropriate ways to spend time.
3. Alexandra thinks that Atticus is not enough of a feminine influence. Furthermore, Alexandra seems to be prejudiced against Cal believing Cal can't influence Scout in a positive way either. Thus, Alexandra takes it upon herself to make Scout wear a dress and go to a Missionary Circle meeting at the Finches house.
Many moms can be overbearing or pressuringly influential. For Scout, this is the type of motherly influence she experiences. Aunt Alexandra doesn't value the individual that Scout already is, but tries to use a woman's manipulation to make Scout into something that she is not.