As they say, there is a first time for everything.
Seriously though, I think it is because 'a first attempt' does not specifically describe her first attempt; it is an abstraction, which is about anyone's first attempt at web design. The overall idea of this, I think, is to make a comparison between what she did designing a web page for the (understood as 'her') first time and what other people do for their first times.
Not a teacher.
Student or Learner