Shih-tzu's are the breed that I have more food problems with than any other!

First you need to check her dentition with the vet. It is very easy to put this down as a behaviour problem when there is really an underlying dental or oral problem.

If that is all clear, and even if it isn't, it really isn't a good idea to leave food down all day.
It is an instant code for the dog to believe that it is the highest status animal in the household. Add to this the fact that she can manipulate your behaviour in how she reacts to her food and the fact that she is a very smart dog and you have....disaster!

If the vet checks out fine I strongly suggest that you remove the food bowl from the floor.
Work out a normal weight per day that you would expect the dog to need. ( I use a washed out can to measure feed rather than by weight so what ever works for you.)
Then set up a ritual and don't deviate from it.
Toilet the dog and have a short play. Get the dog to sit while you measure out a VERY small part of the daily ration - if it works out as only ten pieces of food, so be it, it will be fine - next to the dog food get a very small something for yourself to eat (most of my clients find two or three cornflakes the easiest) and eat them. Ignore the dog during this process, even if she moves away. Don't look at her or speak to her. When you have totally finished eating whatever you have chosen turn back to the dog with the bowl in your hand. If she has broken the sit call her back and get her to sit again. Put her food down, still without a word, and walk away. After fifteen minutes you MUST pick the bowl up even if she has followed you rather than eat. During this time you continue to ignore her - not looking and not talking to her.
You then pay her no attention, not a look, touch or word until she has gone away from you and lain down for at least five minutes.

Then, and only then, call her to you, get her to sit, praise her, and then carry on as normal.

You are taking the issue out of food - there is nothing to be gained in any way from eating or not eating - it doesn't make any difference to you - so when she does eat you react in the exact same way - 15 minutes and then no reaction until she is relaxed for 5 minutes.

This will be very hard for you - if she doesn't eat, and she won't at first, you will feel bad taking the food away and then ignoring her. She will probably demand attention from you so ignoring her will be tough. When she does eat, and she will, your natural reaction will be to make a huge fuss of her and praise her -DON'T!!

Split her meals into the smallest portions you have the time to deal with - bear in mind that there should be at least two hours between feeds.
Increase activity - play and especially simple sit excersise, stay, come - do not reward with food - get excited and put on a high voice and physical praise instead.


Be aware that she may refuse food for several days and that if you start this then the garunteed way to make the dog worse in it's eating habits is to give up!!!

You must do it at every feed.

No tidbits of any kind.

As long as the vet says she is fine it will work - but you have to be prepared to see it through.

Please let us know how it goes, good luck!