Q. 1. My sister had an abortion. Does that disqualify her from being the Godmother of my child?
A. 1. Because of the conditions involved, I cannot answer a simple "yes" or "no" to your question.
First of all, I must say that a sin is not a sin until such time as the sinner knows that his/her actions are a sin. In other words, if your sister did not know that it was a sin to have an abortion, then she did not commit a sin. That is most unlikely... but one must be open to the benefit of the doubt.
Secondly, the Church disqualifies a person who has incurred an (a) "official excommunication" or (b) "latae sententiae," by the very commission of the offense. That means the person (a) was officially told by a member of the clergy of the Catholic Church that she/he was excommunicated or (b) he/she knew that an abortion was a sin that results in an automatic excommunication and that person proceeded with the abortion. Such a person does not qualify to be a godparent.
Now, if the person was excommunicated "latae sententiae", and had the excommunicated lifted and the sin of abortion forgiven through the proper channels, than that person is no longer considered as excommunicated.
Pope Francis has permitted that during the Year of Mercy, all Catholic priests will be empowered to forgive the sin of abortion. During that year, it will not be necessary for the sinner to go to a Bishop to have the excommunication lifted. Under normal circumstances, such is required because members of the clergy (the priests) do not have the faculty (authority) to lift excommunications.
To answer your question, does your sister qualify to be a Godmother? It depends if she had her excommunication lifted or not. Her answer to that question provides you with the answer to your question.