Stupid relationship question: what should I do now (extremely long details inside)

This question may seem stupid to some jellies. But really, I can’t find an appropriate solution, so I have to rely on you. Sorry if this question is just too stupid to be answered.

Let’s go through the scenario first: there’s that friend of mine who used to study together with me at high school and still goes to the same class as me at the moment (let’s call her A). At university, she’s pretty “asocial”. She doesn’t seem to have any intention to make friends with anyone and so do every student in my class (I do sometimes see her talking and laughing with others, but generally it doesn’t seem like she is trying to socialize). The only one whom she clings on the most seems to be me (because I used to study with her). She also has the tendency to skip class or go away in the middle of a lesson while the teacher doesn’t notice, saying that the lessons are “too boring”.

Now to the point: About 3 days ago, A went to class and sit at the table I was sitting. Between us was another girl (let’s call her B). At the break, A asked me what time it was. I gave her the time then played with my mobile phone for a while. When I looked up, A had gone, although her bag was still on the table. B told me A said she had to go out for a while. B was asked to look after A’s bag as A would come back to fetch it at the end of the classes.

We continue to study until classes ended. B picked up A’s bag and went out to wait for A. I took my mobile phone out for the time. Just then I found two messages, which were all from A and were sent at nearly the same time. The first one was: “Could you bring my bag back home for me?” and the second was: “You can take it home. And please bring it to me tomorrow.”

I got pretty irritated after reading the first message, since her home was very far from the school, and I had some work to attend to a few minutes after school. When I came to the school gate, B complained to me how late A was. I said A would never come and told her about the messages. B asked me to keep the bag since she shared her room with some other people and she feared they would explore the contain of the bag before she knew it. I agreed and take the bag back home.

When I came back home, my parents saw A’s bag and ask about it. I told them everything since I was too irritated. They got irritated too. They all agreed her having me bringing her bag back home was a bad idea, and accused A of being “too thoughtless and carefree to think about others”. Nevertheless, they agreed to let me bring the bag to school for her.

The next day I brought the bag to school. A didn’t come (somehow I wasn’t surprised). I ended up dragging the bag back home again. Of course my parents knew right away what happened. This time their endurance ran out. They told me not to bring the bag to school again, and to tell her that I would only give it to her if she came to our home and ask for it back.

And that’s where the problem came in. At high school A and I had some “history” that happened to reach my parents. And most of the time they thought A was taking advantage of my kindness. That means they see A in a very negative light. So it isn’t surprising that they run out of endurance so quickly. Their comment about what happened was that she was just taking advantage of me again, and I really shouldn’t help her. But what they don’t know about A is that she’s very bad-tempered. She gets mad quite easily, sometimes at a very trivial reason. And more than one she get mad at me, and whenever she does, she’s horrible, too horrible for me to confront. I know my parents won’t let me get the bag out of our home, and hiding it is impossible. But I don’t seem to have much courage to tell her straight that I won’t bring her bag for her and she has to come to my house to get it. I think I’m in quite a catch 22 situation. So, what am I to do now?

I don’t have classes until next week. And today she has rung me twice. I guess she mainly wants to talk about the bag. I haven’t rung back yet and I don’t want to, because I don’t know what to say and because I don’t want to confront another of her anger (she even gets mad when she ring me and I ring her back so late).