Holding my breath, I opened the door to my sister Beth’s bedroom, listening carefully to make sure she was asleep before making my move.Her new dress was hanging at the front of her wardrobe – and I’d decided it would be the perfect thing to wear on non-uniform day.Grabbing the hanger, I was about to sneak out when she sat up. ‘Hey!’ she said, sleepily. ‘What are you doing? I haven’t even worn it yet!’‘I thought you said I could… borrow it,’ I whispered.She shook her head. ‘You’re always so mean about what I wear – but you’re always stealing my clothes.’Beth is just a year younger than me, but back then, when I was 12 and she 11, this seemed to be a major age gap.I believed it was a legitimate reason to boss her about and dismiss anything she cared about as ‘babyish’. In fact, I was only ever nice to her when I was persuading her to gang up against our even younger sisters.I’m the eldest of six girls, with just eight years between me and the youngest, twins Maddy and Dotty. Today, I love nothing more than spending time with my sisters. Today, eldest child Daisy Buchanan (pictured on her wedding day) loves spending time with her five sisters, but she says they weren't always close growing up due to her jealousy Being bullied at school took on toll on Daisy's relationships with her sisters, as she felt so small there that she instead 'became the bully' at home to feel importantBut growing up, we weren’t close at all. And that was my fault.The problems began when I started primary school. I was badly bullied, and desperately unhappy.At school, I felt very small. And so at home, where I wanted to be important, I became the bully.All games had to go in my favour, or I wouldn’t play. I didn’t even want to share interests. If they became enthusiastic about something I cared about, I announced it was pathetic, and so were they.Beth was a talented artist and was constantly writing poems. I told her she was a loser, and her friends were losers, too.The truth was I wished I could attract friends as easily as she did. I was bullied for being ‘weird’ – but she was much weirder than me. Yet her personality seemed to work in her favour. At school, I tried to protect her, by telling her to stop drawing attention to herself. However, she didn’t seem to need my protection.Neither did Grace, who seemed to be effortlessly confident, even though she was three years younger than me. Unlike me, Grace forged a close bond with the three youngest sisters, Olivia, Maddy and Dotty. They’d play together for hours. I dismissed their games as ‘stupid’ – but deep down, I wished I could join in. The truth is I was jealous of my sisters. When the twins were born, I felt a strange pang of longing. I thought I’d love to have a twin – someone just like me, who understood me.It never occurred to me I could reach out and have that relationship with one – or all – of my sisters too. With hindsight, Daisy came to realise that her sisters did really care about her and what may have once seemed like immaturity was in fact them trying to impress herAt the time, my sisters didn’t know about the bullying. Life was tough. At school, I experienced constant cruelty. At home, I was always in trouble for being horrible to my sisters. I didn’t understand how to be kind to them, because I was experiencing so little kindness myself.By the time I started secondary school, I’d become increasingly withdrawn. I started to struggle with eating disorders. Just before my 15th birthday, I reached crisis point.After another day of eating next to nothing, I went out for a brisk walk and fainted in the road. I was almost run over by a car – luckily, the driver saw me just in time and called an ambulance. My parents and my sisters were devastated. Their concern shocked me into taking action. My sisters really care about me, I thought. Even though I never show them I care about them. I need to change.It took a lot of time to regain my sisters’ trust, but I made a great effort to forge a relationship. I learned to bite my tongue. Instead of complaining about their immaturity, I realised I was happiest when we could be silly together.And it broke my heart when I realised how hard they had been trying to impress me, and how much my approval meant to them. Years later, they told me they had taken too many of my words to heart.Olivia had stopped listening to the music she loved, because I’d said it was ‘stupid’. Grace had changed the way she dressed because of my sneering.I’d do anything to take those words back. All I can do is tell them how sorry I am, and to celebrate the incredible women they’ve become.Today, aged 41, I’m so grateful for the relationship we have, despite our rocky start. They’ve helped inspire my new novel, All Grown Up, a contemporary retelling of Little Women.I have them to thank for much of my happiness. When, after a string of terrible relationships, I met the man I’d later marry, I told Grace I wasn’t sure it would work out. He was considerate and early for dates – surely, he was too keen?‘He sounds very kind,’ said Grace. ‘And you should be with someone kind. Kindness is the most important part of any relationship.’She’s right. I only wish it hadn’t taken me so long to show kindness to my own sisters. To understand that they’re worthy of kindness – and so am I.All Grown Up by Daisy Buchanan (Century, £16.99) is out now