I have a 16-year-old sister who is acting out in ways that seem odd. She does not have a lot of friends, but does have one particular friend, who has just got a boyfriend. I am 28 and have been away from home since I was 18. I live about two hours away, but don’t drive so it is hard for me to visit her. For a while now, she has felt the need to be rude or mean to everyone – family and friends.

She seems angry, but not a normal teenage angry. I remember being her age. I rebelled and did everything you probably were not supposed to do. Somehow, I turned out OK after about the age of 25. My mum would provide all you wanted, but the more intimate part is never there. My sister has expressed this to me before.

My mother and stepdad divorced a while ago. He now has two babies of his own and is still a huge part of my sister’s life. My mother remarried as well, and is maybe not as involved. She is there, but a little bit more involved in other things. I feel maybe there is some sense of loss in my sister, of not belonging. I know that is normal for someone her age, but the things she says make me worry. For example: “I don’t like people!”; “Yeah, I am a mean person, so what?”; “If they look at me the wrong way, I’ll … [be mean/hit, etc].”

It worries me. She is already seeing a counsellor, but nothing seems to be changing, just getting worse.

Do you have any thoughts on how to help? I feel as if she hates me, our family, the world, everyone …

You are very astute. And you will probably be your sister’s greatest ally during this. But although you having “been there and done that” will give you insight, her journey, exact circumstances, and therefore reactions and “acting out”, are going to be different from yours.

I think she is really lucky to have you around. I contacted Helena Cowen, a child and adolescent psychotherapist (childpsychotherapy.org.uk), who immediately picked up on what you also mention: the tremendous sense of loss in your sister’s life. She thinks that, probably, your sister’s friend getting a boyfriend has triggered a sense of loss in your sister.

“First,” says Cowen, “you have more awareness of your sister’s problems than you may realise. Your sister is dealing with several constellations of family and probably feels cast aside, most recently by her friend. If you think about the attachment young adolescents have towards their boyfriends, it is hard to regulate the feelings, it’s very intense – your sister probably feels really left out [of her friend’s life now].”

Then we add into that your stepdad remarrying, two new children, your mother not really being there for the emotional stuff (where does your sister live? With whom? You didn’t say), and it is not surprising that your sister is so destabilised.

She is very probably rejecting people because she feels so rejected herself. It takes confidence to make yourself vulnerable, and confidence comes from feeling secure.

Cowen suggests that you don’t panic, but allow your sister some time, both to find her way through this (after all, you turned out OK) and for the therapy to work. “Therapy can often bring distressing feelings to the surface to begin with,” she says.

I would also suggest reaching out to her in whatever way, or combination of ways, works best (and that may change), either with regular phone calls, letters or Skype. These points of contact will matter to her even if she doesn’t always respond. And even if she gets angry (she may test you to see if you, too, will stick around if she is “mean”). You don’t have to write reams, just let her know you are thinking of her. I note you said that it is not easy for you to get to her, but I wonder if you could see her every now and again and fix these dates in stone so that she knows she has that to look forward to?

“You know what she’s missing,” says Cowen, “and you can help her to make sense of it. And her therapist can help your sister to realise that having those feelings does not make her a bad person. That it is possible for her to love her family/friends, but also be very, very angry with them.”

Cowen says not to forget that adolescence is a very intense time and things are felt very acutely and don’t “always calm down until your 20s. Indeed, there is some evidence that the frontal lobe doesn’t finish developing until the age of 25/26.”

Don’t forget to have fun with her, too, says Cowen. Perhaps when you meet up you could do stuff together, silly stuff as well as having good chats?

Adolescence can be a hard enough time as it is, but your sister sounds a bit at sea, as if (you said this yourself) she doesn’t really know where she belongs. I wonder if you have spelled it out to her that you also found things tough when you were a similar age, but you feel much straighter and calmer now? Sometimes we all need to know that difficult times will end. Also, remember that teenagers often look as if they are not listening and don’t care. But they are, and they do.