Not to quibble, but I don't think that's quite right (CCC 1267-74). My understanding is that ANY legitimate baptism (i.e. trinitarian formula as in Mt 28:19) configures the individual to Christ. Her baptismal seal was recognized by the Church (along with the vows of parents/godparents) as incorporating her into the Catholic Church. But the baptismal seal itself wasn't a Catholic mark per se. Rather it was administered by God during a rite performed by a Catholic priest. This is why most nonCatholic converts aren't baptized when brought into full communion with the Church at the Easter vigil. It's only required for the unbaptized or those baptized in traditions that don't use a trinitarian formula.
The Church may always consider Palin a separated member but that's because she once attained membership via her indelible baptismal mark and the vows made. It isn't because that baptismal mark contained something uniquely Catholic that's absent in valid nonCatholic baptisms. The Church would always consider me a separated member too if I, as a convert with a nonCatholic baptism, renounced the faith (God forbid!). At least this is my understanding.
| 1272 Incorporated into Christ by Baptism, the person baptized is configured to Christ. Baptism seals the Christian with the indelible spiritual mark (character) of his belonging to Christ. No sin can erase this mark, even if sin prevents Baptism from bearing the fruits of salvation. Given once for all, Baptism cannot be repeated. |