Dd is 6 and is morphing into a tiny Kevin the teenager. Until now she was extremely shy and timid but overnight everything is "but whyyyyy?" "it's not fair" "but I want it etc." She will constantly ask for things like sweets, toys, or days out and strops when she doesn't immediately get it. Complains constantly (I'm hot, cold, hungry, etc) and NEVER stops talking.
I know all of this standard kid stuff, so why am I struggling with it so much? I know I'm projecting as I had a horrific childhood so it almost makes me angry that she doesn't appreciate that she has a safe, warm home full of toys and nice things. She has started answering back too, and I'm struggling not to snap or react angrily 
I know the problem is me and I need coping skills. I did brilliantly up until now and got through the difficult baby and toddler stages by myself. Now that she's old enough to challenge me I'm failing her. I'm terrified of turning her into a anxious people pleaser like myself.
Any tips, book recommendations or organisations I can turn to would be gratefully recieved. Ex dp is not in the picture and no family to rely on unfortunately.