Warning, a self pitying post!
A bit of background. Dsd2 lives full time with dp and I and has done for 2 years. I've lived with dp for 4 years and been with him for 6 years. His wife left him for another man 8 years ago and has had several boyfriends since.
Dsd sees her mum (something we insisted on when she said she wanted to live with us) but it's only 1 day per week and it's not a close relationship.
I don't consider myself to be dsd mum, but I do feel I an the "second parent" to her. It is me who goes to school performances at her request, takes her to the doctors, listens to her tales about school life, knows what food she likes, knows when she has her period, has had the contraception talk etc etc.
Generally dp is first port of call and I am there if he can't do something for her.
So Tuesday night was her school prom. 
Her and her prom date are at the front of the house and all the extended family turn up to take photos. Dp and I had already discussed making sure we got some photos of dsd without her boyfriend so that we could still display them in the future just in case she's still not with her boyfriend.
Dp nor any of his family suggested that dsd have a photo with me. She had photos with boyfriends family and extended family but right at the end I had to ask dp to take a photo of us.
It's not dsd fault, she was overwhelmed with it all. Ironically it was me that was chatting to her when everyone else had forgotten her and was chatting between themselves.
I am a quiet person and not very forthcoming but even so, I would have thought someone would have at least thought it would be nice for dsd to have a photo with me. 