If you write it that way, it'll sound like 'teshi'. the 'i' will be short. But since you pronounce Tessie with a long 'i', I think it should be written with a -, or |
But I'm not really sure if it should be written テシー　or テッシー. But that really just depends on the pronounciation...

Okay i will stick to
テ
シ
|
then......

I tried to write her name in western letters but it just doesnt seem to fit the tattoo.... I really think it needs the katakana characters.

Well bout the pronounciation actually her name is Tazzie... but i am dutch.. So if u say that name it will sound like tessie in english...

You should know you're playing with fire here. Pronunciation is the only thing that matters to transliterate to Japanese, and if the pronunciation is even slightly different than what you're saying, you're going to get something that is wrong. This is why getting a Japanese tattoo with advice from people over the Internet is objectively stupid.

Sorry about your dog, though, man.

I have to agree with this. I am less convinced now than I was at the beginning that this is the right transliteration of your dog's name in Japanese.

Unfortunately, I cannot hear you say the name to know if it is being arranged correctly in Japanese.

Yes, you need to use the "chouon mark" there but what you have is the kanji for "one", which looks slightly different. Note that the chouon mark turns and goes down in vertical text. If you prepare your text using Microsoft Word and turn it vertical, you should get that done automatically if you have used the right character. (Microsoft Word is one of the better computer applications for preparing Japanese text correctly.)
Sorry, I'm not fond of tattoos myself, especially ones in Japanese. But it's your decision. :ywave:

No, you still are using the kanji for "one" instead of the "chouon" character at the end there.

In case you're wondering how I came to notice all this stuff, I used to go to a calligraphy class, and the first thing the teacher did was to make me write "one", "two", "three". I did them each about a hundred times I think. So I got quite some idea of what the kanji for "one" looks like. I couldn't find any "ones" but here is a memento of those classes (the teacher's corrections are the orange ink):

Regardless of mistakes, your calligrapy is so much better than mine. I could never get that dern brush to go where I wanted it to. :/

Well u can :)
tessie.mp3

I tried to change it into the right mark.
Is this better?

Listening to the file and looking at this, I think it is as good as you can do.