Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am very sorry to hear that your girl appears constipated and I'd like to help.
Are you sure that she is constipated (hard, dry small pebbled or large, hard to pass stools)?
Dogs with diarrhea will strain repeatedly as they feel like the have to go because of the irritation but they may only produce a little very soft or liquid stool.
If she has diarrhea rather than constipation then I can give you some suggestions to help with diarrhea.
I would not feed her any food for 24 hours. This should help stop gut spasms and restore normal gut motility. Small amounts of water or ice cubes given frequently are fine as she needs fluid. You can give her pedialyte to replace electrolytes too, but Gatorade is much too high in sugar which can make her colon irritation worse.
Today even with the fast for diarrhea you can start Kao-pectate at 1ml per pound or 1 tablespoon per 15 pounds of body weight every 6 to 8 hours. This is quite safe and will coat her irritated gastrointestinal tract as well as absorbing bacterial toxins. You can use it for several days until her stools look normal. You can find kao-pectate at the drug store.
If she has a tense painful abdomen, continues to have diarrhea with no improvement after being on kao pectate for 24 hours, becomes very lethargic, begins vomiting or runs a fever greater than 103.5F then she really must be seen by a veterinarian as soon as possible.
After her food fast start a bland diet of 1/3 boiled, lean hamburger (or boiled, white, skinless chicken), all fats and juices drained off the meat, mixed with 2/3 boiled, plain white rice. Feed several small meals a day. You might wish to add 1 tablespoon of canned pumpkin to each meal if you see mucous in her stools as fiber helps soothe an irritated colon.
Once she feels better (no diarrhea for 48 hours) start mixing in her regular dog food very slowly. Less bland more regular with each day. It should take a week or so to convert her back.
However if she is indeed constipated, having difficulty passing firm, dry, very small or large stools, I can give you some recommendations as well.
If she is still eating and drinking normally and not vomiting there are a few things we can do to help her.
One is to increase fiber by adding canned pumpkin (not pie filling, just pumpkin) to each meal. One tablespoon to each meal for a small (poodle or shih tzu sized dog) to 2 tablespoons to start. This can be used long term to help keep things moving and avoid constipation.
These are just guidelines, you can adjust the amount based on her ease passing stool as well as whether her stool is too soft.
If you have Miralax you can use that instead of the pumpkin. Sprinkle 1/8 th 1/4 of a teaspoon on her meals. If you use Miralax make sure to increase her fluid intake as it works by drawing fluids into the intestines and can lead to dehydration if her fluid intake isn't increased enough.
I do not recommend Milk of Magnesia as that is a stimulant laxative and can cause abdominal pain, cramping and interfere with electrolyte balances. If there is obstipation (hard dry stools stuck in the colon) it can be dangerous and lead to rupture.
Increasing the amount of fluids in her diet in general will help as well. You can add low salt chicken or beef broth to her food. The more fluids she takes in the better so if she likes to lick ice cubes give her those as well.
Slow walks can also sometimes help to get the intestinal tract moving properly.
If she is vomiting or no longer eating we are probably beyond home therapy. She needs to see her veterinarian. But you can use the above tips for preventative measures in the future. And if she seems to have chronic troubles with constipation pumpkin or Miralax can be used chronically if needed.
For either diarrhea or constipation you might also wish to add a probiotic to get her gut bacteria back to normal. Fortiflora or Benebac are two very good ones.
Please let me know if you have any further questions.