Sue Ellen deserved that slap by implying Pam was a kept woman or a prostitute. She was beyond mean and nasty in "Survival," not only to Pam, but to Lucy. She had a lot of nerve trying to stop Lucy from contacting Gary, her own father. Gary had a right to know what happened to his brothers. Lucy should have slapped Sue Ellen as well. Pam wasn't perfect and may have deserved a slap from Jenna when she offered to adopt her baby, but Sue Ellen was often intentionally malicious to people who tried to support her such as Bobby and Pam. That said, I also liked that they showed Sue Ellen's vulnerable side after the slap, and that Pam and she got closer after that. Sue Ellen was definitely complex but often despicable, at least in the early years.