Much of Diamondheart's history is unknown. She was probably among the first citizens of Xaviera. At some point and for unknown reasons Emma changed her code name from White Queen to Diamondheart. As one of the last surviving X-Men, she has seen many of her friends and comrades die; mainly at the hands of Dust. Diamondheart specifically mentions that Dust killed her lover - presumably Scott Summers (Cyclops).
Diamondheart now remains in her organic diamond form most of the time. In this form, she was far less vulnerable to attacks. However, it appeared Emma Was still unable to access her telepathic abilities in her organic diamond form.
Diamondheart also has taken on the care of the decrepit Ink. Ink couldn't or wouldn't speak, and for unknown reasons Diamondheart didn't use telepathy to communicate with him (possibly because of her unwillingness to change from her organic diamond form or his lack of consent).
When Dust attack the remaining X-Men at X-Men Tower on Xaviera, she murdered Diamondheart by creating a whirlwind around her thereby suffocating her.