I watched this anime 1-2 years ago but can't remember the name. I would like to watch it again. Judging by the style of the anime it is quite new, I would say no more than 5 years old. The story is about a girl in her teens living with her father. Illness isn't quite the word for it, but her growth has stopped resulting in her looking like a 1st or 2nd grader. She falls in love, but I don't remember how that ends. As she is a teenage girl, she is very cautious of fashion and her main problem is finding clothes that she likes. In the end she start designing clothes for children and people with the same problem as her.
To my knowledge, it is as someone already mentioned, The Friendly Winter.
A 19 year old girl with a rare growth disorder that leaves her in the body of a small child meets a boy with a mental disorder, who has the mind of a small boy in a 17 year old's body. A Friendly Winter shares with us the endearing story of their day-to-day lives, joys and tribulations.
You might have mistakenly remembered it as an anime because it is fully coloured. It is actually a Korean Webtoon. Her hair is close enough to be misremembered as pink.
In the end,
she is proven a capable business woman who runs a children's apparel fashion line.