This is an interesting question because although Miss Emily might be considered a "strong" person in lots of ways in the story, it is clear that her "strength" is also linked to a crucial weakness, which is her tendency to retreat from a reality that we are not comfortable with into a former world or a fantasy world where we get everything our own way. Consider in the first section how she greets the Alderman and then deals with them, insisting that she will not pay taxes:
She did not ask them to sit. She just stood in the door and listened quietly until the spokesman came to a stumbling halt. Then they could hear the invisible watch ticking at the end of the gold chain.
Her voice was dry and cold. "I have no taxes in Jefferson. Colonel Sartoris explained it to me. Perhaps one of you can gain access to the city records and satisfy yourselves."
She is clearly a "strong" character in the way that she is able to face down the authority represented in the alderman - she will not suffer fools gladly. It is clear however that this "strength" as illustrated here is likewise a weakness, for it is indicative of the way that Miss Emily has retreated into her own world and will not let reality enter. Note the reference in the first paragraph of the quote above to the "invisible watch," reinforcing the idea that Miss Emily is linked with the inexorable passage of time. It is as if she keeps her own time regardless of the rest of the world, and thus can talk as if Colonel Sartoris is still in power, whilst the text tells us that he died ten years ago.