Sorry for the delay.
This a very good tease-story and very good first try.

You built up your story and when you had the readers where you wanted us – you stopped with a just a hint at further action, letting the reader build up on it. That is how the tease stories are done.

You have some expressions and word usages, which probably would not be used by native English speakers. For example: people are 2 or 3 cm shorter then others, not smaller. However, the only way to learn that is to write more. Please do so.
There are some repetitive cadences in your narrative. Some of them are good – but some are not so good. I suggest you change: “She told her that she is a secretary too, but Rebecca was shocked when she learned about Emma’s second job. Two years ago she had found a really exciting job.” To “She told her that she is a secretary. However, Rebecca was shocked when she learned about Emma’s second job. Two years ago she had found a really exciting one.”

Do not be afraid of shorter sentences and simpler expressions, that does not make the story simple. You can compress it too. For example:
“Rebecca was shocked after Emma finished her story. But only for a moment” to “For a moment Rebecca was shocked after Emma finished her story.”

If I was nit picking I could say that there is too much description versus narration in this piece but since it is obviously an opening for a longer piece and a teaser, it worked just fine.
Great job.

In fact, I think your new assignment should be – more explorations of Emma and Rebecca. but maybe in some unexpected direction.