Step sister

Your mother and father were fighting for months, but they finally divorced, your father then met a new woman about a week ago and she is also divorced, she has a daughter about your age and a younger son, you have seen the mother, but not the kids yet, today is your first time seeing them.

The mother presents her children to you and your younger sibling, and then she tells you to go and play upstairs
The girl seems interested in you...
She says:

Hi, my name's Elisa, nice to meet you!

.