CALGARY, Alberta (AP) _ A teen-ager in her 19th week of pregnancy underwent an abortion after Alberta's Court of Appeals threw out an injunction obtained by her Mormon parents.

''That was probably the hardest thing I'll ever have to do but I'm glad I did it and I hope it will make things easier for other teen-agers who have the same problem,'' the 16-year-old girl from Medicine Hat, Alberta, said in a telephone interview today.

She said she underwent the abortion Wednesday at Calgary General Hospital.

A court order blocked the use of the girl's name because of her age.

Three members of the Alberta Court of Appeal deliberated for about an hour Wednesday before deciding the girl was mentally capable of making the decision to have an abortion.

Justice Kenneth Moore of the Court of Queen's Bench had issued an injunction blocking the procedure at the parents' request last week. It was believed to be the first time guardians have challenged a dependant's legal right to make such a decision on her own in Alberta.

Justice Roger Kerans of the appellate court said Wednesday that he believed the girl was making the wrong decision, but added: ''The question is, can the parents and the courts impose a decision on a 16-year-old?''

The abortion lasted 16 hours because of the advanced stage of the pregnancy, the girl said. After 13 weeks of pregnancy, abortions are performed by inducing labor by injecting saline solution into the womb.

The girl said she realized from the beginning she wouldn't be emotionally prepared to have a baby and then surrender it for adoption.

''I couldn't afford to keep the baby and neither could my parents,'' she said.

She expressed anger that she had to struggle against her parents and go through a court battle to obtain the abortion.

''If I could have had it right away, it would have taken only a few minutes, not 16 hours,'' she said. ''The system is really unfair.''

The teenager's mother said, ''Of course we still welcome her into our house.''

But she added, ''Every teenager all over Alberta knows they can go against their parents now because it's been proved in court.''