The main plot around Resident Evil: Apocalypse centres on the characters having to find Angela Ashford in Racoon City so that her father, Charles Ashford, will tell them how to escape with his daughter. They manage this and at the end of the film when the group takes Alice out of the Umbrella facility Angie is seen in the back of the car.
However, in Resident Evil: Extinction Angie is missing and no explanation is given to her whereabouts that I am aware of. Of course quite a bit has happened since then, with the group splitting up and Jill Valentine presumably being taken hostage by Umbrella.
There is some mention to an incident that happened in Detroit so presumably something could have happened there to her.
White Queen: Her powers would appear to have grown at a geometric rate since her escape from the Detroit facility.
[...]
Carlos Olivera: Alice, what happened to you? Why did you leave after Detroit?
Alice: I didn't have a choice. They were using me.
Carlos Olivera: What do you mean?
Alice: They were tracking me. I couldn't be around you. Any of you. I would've gotten you all killed.
Carlos Olivera: That's why you disappeared?
Alice: Broke into an Umbrella facility and hacked into their computers downloaded the satellite trajectories and stayed off the grid.
Resident Evil: Extinction
What happened to Angela Ashford?