But.. Does a shih tzu need to be in full coat to compete?

Yes.
Unless you are showing at non regulated 'fun' shows, or KC companion shows (aka Exemption).

I did think that would be the case. My partner doesn't like the show coat look he thinks they lose the cute factor and look like 'dogs in dresses' lol so I'm starting to doubt ill be showing her anytime soon!!

Doesn't mean you can't show your dog, just means not at KC competition shows. She would have to be KC reg and ownership transferred into your name for that. From what you have said in other posts, she may not be of the right type anyway, if she is smaller than usual. But you can show her at fun shows and companion shows where they are judged on condition, temperament and character instead.

Well you could show at KC shows but you are not likely to get anywhere. She may be a really stunning example of the breed and if she is the odd judge may place her but your would then have to face being told what a terrible thing you had done to your beautiful bitch.

Any pure bred registered dog can be shown at a KC show despite what you do to it - except you can operate to change the appearance or to correct a fault the dog was born with.

Just re-read your first post -

But.. Does a shih tzu need to be in full coat to compete?

The answer is she will not be competitive - you can enter her but that is not what you asked.

I know she would never place very highly due to her being smaller I just thought she would probably enjoy the day so fun shows would be the way forward. She's a very good agility dog fast and intelligent so maybe that's the route to go instead of shows she would never do well in. She is KC reg and I am her registered keeper but I didn't breed her so 'I' haven't made her smaller than normal just to clear that up. Not did I buy her because she was a 'teacup' size. That's just how she's ended up. I don't want anyone to think badly of me that I've purposefully bought a little one or anything like that!

Also Nova what do you mean by "being told what a terrible thing I've done to such a beautiful bitch"?

They mean that if you took your cut girl to a formal dog show as it were some people there would consider cutting the coat off as a terrible thing to do, Especially if your girl was a good enough example to get placed. As the coat is the main feature of the breed and there are many people who think they shouldn't be cut off. So if you entered her in a formal show (which you could do) some people might voice there option, but the coat wouldn't matter at a fun show as its just for fun.

But then again would a judge in a formal show accept a clipped one as it surely wouldn't meet the breed standard for the coat?

They mean that if you took your cut girl to a formal dog show as it were some people there would consider cutting the coat off as a terrible thing to do, Especially if your girl was a good enough example to get placed. As the coat is the main feature of the breed and there are many people who think they shouldn't be cut off.
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That is exactly what I meant.

If you just want to attend fun shows then no problem as you can show any dog at all it does not have to be a pure breed and can be clipped out as the classes are not conformation classes.

>Does a shih tzu need to be in full coat to compete?

The section in the breed standard on Coat says: Outer coat long, dense, not curly, with moderate undercoat, not woolly. Slight wave permitted. Hair not affecting the dog's ability to see. Length of coat should not restrict movement."

So if her coat isn't long then it will obviously count against her in breed shows. For companion shows or agility etc it won't matter a bit.

Try some companion shows - they are great places to learn. Nobody will mind if you have her in a pet trim instead of long coat, and you can learn how to handle her and stand her for the judge without worrying about it being too big and formal a show. If you like it and she does well, you can always start sneakily growing the coat little by little......

Some of the bigger companion shows and 'all about dogs' type shows run have-a-go agility as well, so that gives you another thing to play with!

If she enjoys and is good at agility she may well enjoy that more than showing. Although many dogs enjoy showing it does involve a lot of waiting around for that short time in the ring. Fun shows ( companion) are a great way to have a go and see what you both think

There are many ways to enjoy your beautiful Shih Tzu in pet trim, but I would not recommend you invest in the entry fees and the associated travel expenses to enter the KC Open or Championship show ring, as a dog needs to be in full coat for this type of show.  The only time I think it would be appropriate to enter is at certain Shih Tzu breed club shows where they do actually schedule a class for Shih Tzu in pet trim.  The entrants are usually dogs that have been retired from the show ring and have been clipped off, but you could enter those classes if you wished. Unfortunately they are few and far between.
On the other hand what you could do is enter the fun type shows, do agility and try obedience classes.  I have a small Shih Tzu who did not make the size required for the show ring and so he is clipped off and we go to obedience classes and he works with me as a Pets As Therapy dog and we have a great time. Good luck and enjoy your Shih Tzu.  

>Not did I buy her because she was a 'teacup' size

There is no such thing as a teacup dog.

Don't know if the breed club shows may have classes fro clipped off or stripped down dogs?  Sometimes happens in American Cocker shows - and we have had a CC winner who was clipped out ( a few years back) but he was an exceptional dog.  So it comes down to the hwole picture, and I have to agree with the others, would probably be a waste of entry fees.  Companion shows can be fun, and a good way to get into showing and learn the ropes.