my line of thought would be:
-is the tumour going to cause the pup any negative effects (eg: annoyance, pain, itching, other risk to her health) if you leave it alone? if it keeps growing, i think it will.
-is removing it going to negatively affect function of the pups ear (hearing, etc) more than leaving it would? i don't think so, if the vet is recommending it.
-is the pup going to give a monkeys when she looks in the mirror and sees that a bit of her ear isn't there? is she going to be all ashamed amongst the other pups and want to grow her hair long so they can't see it, and feel all inadequate? i doubt it very much. she's not a person.
-if the vet says it needs to go, it probably does. if i'm worried about my pup not being so pretty when she's done, i need to remember that she's not an accessory who is around for my aesthetic gratification.