Am I being unfair to my friend?

Okay, so my 2 best friends and I have been friends since grade 6 - we're in the 10th grade now. Just this year though, on of my friends (we'll call her A) transferred to another school. We always have a ton of work, so we can only see each other on the weekend. However, she has changed completely; all she can think about is getting a guy, and a lot of people call her slutty and desperate. At first me and my to herr friend (we'll call her E) ignored this, but then when we hung out with A, she would only talk about herself. E's parents are kinda abusive, and the other day her mom threw something at her. When E and I told A about this, she was like "awww poor baby i'm so sorry! anyways, do you guys want to come to my school tomorrow?" I'm going to E's house in a few days, the same day A wants me to hang out with her; however, I made up a lie and said I couldn't go, but knowing A, she'll find a way to make me. So am I being unfair for lying to A? Please help!! Thankyou..