Substitutes for Celery in Mirepoix/Soffritto

Hi all, Simple question, I cook for myself and my sister a lot, but my sister is allergic to celery. I want to experiment more with mirepoix/soffritto because I like to make a lot of Italian and French style flavours, but if I put celery in it, she can't eat it. If I'm aiming for the same kind of aromatic flavour base, what could I use instead of celery? I've heard people suggest leeks in the past, but also heard other people say that since leeks are in the onion family that might make it too oniony. Any advice on that? submitted by /u/AbbyRitter