When aunt alexandra speaks of people being "trash," she's referring to

because of all the immigration, america became one big melting pot. the diversity of cultures from all over the world made america somewhat divided as well. people that immigrated stayed with their kind, and their traditions, while native born americans stayed with their kind and their traditions. normally, people born in american scorned the immigrants as well. the new religions also divided america. in summary, it took away from the american culture and identified america as the "melting pot."

the right ones are in bold.

daintly refers to the fact she was reaching for what she ate, not necessarily what she is like.

greatest charm as in she possessed (=had) the greatest charm.

pleasant (her demeanor)

speaking (of her sensibility)

dead refers to the hypothetical mouse.

bleeding refers to the hypothetical mouse.