I was Episcopalian before I am Catholic. There is no easy answer to what they believe, and thus, how are they different, because one of the things Episcopalians pride themselves on is unity of worship, but not necessarily unity of belief. Now that might not seem different than the Catholic Church, but with the Church, there is an official position on many things that are left open in Episcopalianism.
One such thing is the Eucharist. Laying aside the objective reality that they do not have a valid succession, and thus not a valid priesthood, many (not all) do believe in the Real Presence and many do not. Similar to Catholics, except that the Episcopal community does not have an official position. They believe in the real presence, but leave it at that. Is it merely spiritual? Is it substantial? What does “real” mean?
Same goes for women priests. There is no such thing. But Episcopalianism leaves it up to each parish to decide what they believe about it.
Same goes for homosexuality. Each parish decides what its official position is, probably depending on what the priest’s personal opinion is. Your sister is concerned about priestly scandal. A very small minority of Catholic priests, against all Church teaching, behaved improperly. It is completely permissible within the Episcopal community to be an actively homosexual priest, and remain in good standing. It’s like jumping from the frying pan into the fire.
But maybe your sister doesn’t have an issue with homosexual acts, or women “priests”, or gay marriage, or contraception, or gay actively divorced and gay bishops, or divorce, or no apostolic succession etc.