Meanwhile, the Japanese Empire would have had free reign in most of Southeast Asia and the Pacific.
If Edith Keeler delayed or prevented US involvement in WWII, that necessarily means she delayed or prevented the attack against Pearl Harbor, and/or other Japanese aggressions against US possessions such as the Philippines. She could not have held back her country in face of such offensives.
If anything, the Japanese would have had less success in the Pacific... Although if Stalin were tied up with a German advance that in turn was not burdened by a second front, then Japan might opt to advance against Siberia despite the disasters of 1939. The elimination of western Europe as a colonial power would not have made Australia or the Pacific particularly vulnerable as long as the US remained a factor - and Edith could not plausibly have succeeded if Japan did move against the US.
OTOH, the events of ST:FC were such touch-and-go that any tiny disturbance, such as the absence of "Magic Carpet Ride" from the history of popular music, could have spelled total disaster. It probably doesn't take much to prevent the formation of the Federation if a timeline meddler really sets his or her heart to it.