Maybe just an "Obi-Wan killed her" line can be done with mixing some Palpatine's lines and used on one of the shots of Vader (emperor as voice over), hope I make myself clear...! ;\
But it would be hard to believe, even for Anakin, that Obi-Wan killed a pregnant woman... God it's tricky...
And maybe pointless if we can find a more radical change for the end of ROTS.