I think it will save her a lot of trouble in school etc. if you use two S's because according to phonetic rules it needs two consonants to be a short e, otherwise who knows how often it will get mispronounced! With two S's there will be no question how it should be pronounced.
As the parent of a child with a different name I can't tell you how frustrating it is for them sometimes.
I really like the name Tess. In fact I had planned on naming my next puppy that to name my new puppy that, but then when you announced you were naming your baby that I decided I had better not
. Still haven't thought of a name for her, poor little girl! She is already 8 weeks old!
