All they should do is add a coin that will drop instead of an item if you already own it (instead of nothing as currently happens), lillith token for example and if you get 5? you can trade them for any other items she drops.

The problem with Lillith isn't the low drop rates, the problem is that as you get more items it gets harder and harder to get the final part. Cause you could do a hundred runs and just get all the bits you already have.