My little summerhouse has upset my neighbour. Do I need planning permission for it?

I’d intended to use my 2.4m by 2.1m building as a painting
studio. I don’t want to get into an argument, but the complaint
is spoiling my enjoyment of it

Q I have recently had installed a small 2.4m x
2.1m summerhouse at the bottom of our terraced garden. The height
is less than 2.5m. I wanted to use the building to enjoy our garden
and as a painting studio.

Unfortunately my neighbour is unhappy about it. She says the
windows face her kitchen and bedroom. I can’t actually see into
her kitchen as we have a high fence and the garden slopes down. I
can only see her bedroom window if I look up.

Source: FS – All-News2-Economy
My little summerhouse has upset my neighbour. Do I need planning permission for it?