When she was in the thieves' guild she had a book you need for Corinna's summoning quest, after that she is pretty much irrelevant. If you did not save Corinna from the demon when you first entered her house, you would miss completing that quest anyway, which only gives you a little experience and a level of Banish. I assume you killed Penumbra because and was hanging around the park refusing to talk to you after Corinna died. After freeing Penumbra (not sure if you also have to get the book first), you could have gotten a little experience by asking for 'special treatment' under the hatch in Leptine's shop.
