Similar problem here. She is not so bad with washing, but she does prefer to do it herself. Brushing is a nightmare, most days I just give up, but that makes it worse for the next day. We have Gaia baby detangler and spray that through her hair to help with the knots. Sometimes she is happier with us brushing her hair when we spray it. So if you have not tried a spray I suggest giving it a go.

She is so happy though for others to brush it, cut it and plait it. So annoying. I am so tempted to cut it off like Lulu has suggested. I am sick of the fights and the scruffy look she always has due to it.