Hello, I'm Dr. Deb and will do my best to help with this concern about Rosie.
There could be any number of possible explanations for her behavior which range from dietary indiscretion to internal parasites to IBD to a viral/bacterial infection....just to name a few possibilities. But, regardless, the following is what I'd suggest:
1. Feed a bland diet of 1 part boiled, skinless, boneless chicken breast (or boiled lean hamburg) to 4 parts 20-minute white rice. Feed only a smal lamount of one time, 3-4 times through the day. I would not feed any regular dog food. And, you don't have to withhold food for any period of time like you would if she were vomiting (in case you were wondering).
Once the stools start to firm up (if they do, of course), then slowly transition over to the food you normally feed: 25% bland and 75% kibble for 3-4 days, then 50/50 for a few days and then 75/25 for a few days and then 100% dry kibble.
2. If she is not currently taking any nsaid or steroid medication and is not vomiting ,then you can give Regular Strength Pepto Bismol. The dose would be 1 teaspoon per 5 lbs of body weight twice a day.
It may change the stool color to a gray-black or greenish color though so this shouldn't concern you if it happens.
Pepto bismol should not be given to vomiting dogs since it contains salicylates (the active ingredient in Aspirin) which can irritate the stomach.
Note: I'm not familiar with Venylactic P and couldn't find it listed; I suspect it contains steroids, though, which would mean that Pepto Bismol shouldn't be given if this is the case; you'd basically be doubledosing her with medications which might cause gastric ulceration.
3. I'd start her on a good quality, canine probiotic such as Forti Flora or Resources Protegrity GI. These products can be extremely useful for gastrointestinal issues (and to help strengthen the immune system as well). They may be available at local pet/grain stores or can be purchased online.
4. Increase water consumption to help prevent dehydration. You can offer Pedialyte (although some dogs don't like the taste of it) which can help to replace electrolytes lost in the diarrhea.
If the stools don't start to firm up and/or she worsens in any way, then a vet visit may be wise; it's possible that she'll need anti-diarrhea medication from your vet before improvement is seen.
I hope this helps, Deb