Let me ask, is it specifically stated in whatever source this is from that this is Saber Alter? The ahoge being there would lead me to believe otherwise.

Look at the eyes. Saber Alter has yellow eyes. Saber has green eyes.

"Her eyes look yellow" shouldn't be enough to say this is Alter. She lacks Alter's lighter hair color, white skin pigment, she has an ahoge, and she's wearing normal Saber's underdress.