Very good point! Yes, Guinan wouldn't be asking Geordi about Tasha if she had known Tasha for a long time.
In the "mentioned universe" Guinan apparently was not the driving force to make Tasha go back in time. But the sour face "our" Guinan made when she told Picard in "Redemption II" that he was responsible, seemed almost to me as if she were blaming him for the grim fate of a good friend of hers. YMMV.