Gum color sounds normal which is good as is the fact that she's not terribly lethargic.
In general, I don't worry too much when a dog's looser stools contain a small amount of blood; typically this only reflects an irritated colon and nothing more. While it may look alarming, it's not usually very serious.
But having said that, if there's a profuse amount of blood, then I do worry that the patient may have a condition call HGE (Hemorrhagic Gastroenteritis). https://www.vetinfo.com/hge-dogs-explained.html
This condition can be quite serious and usually requires immediate attention.
At this point, it's difficult for me to know if she might have such as serious condition although if she's not terribly lethargic, if she's not vomiting and if she appears to have a decent appetite, then there could be other causes for her symptoms: Dietary indiscretion, viral/bacterial condition, internal parasites are just a few of the possibilities.
Since she doesn't appear to be in a really serious way, the following would be my suggestions over the weekend. If she worsens in any way, then you can always have her seen.
1. Feed a bland diet of 1 part boiled chicken (or hamburg) to 4 parts 20-minute white rice. Feed only a small amount of one time, 3-4 times through the day. I would not feed any regular dog food. Just an fyi, I don't tend to withhold food from dogs with diarrhea issues but I do when they're vomiting.
2. I'm not certain if you have the brand name Pepto Bismol in the UK but you probably have other products which contain Bismuth Subsalicylate which is the active ingredient. As long as she's not vomiting nor currently taking any aspirin or nsaid products then you can give this to her.The dose would be 1 ml per 10 lbs of body weight 2-3 times a day.
For example, if she weighs 50 lbs, then you would give 5 mls or one teaspoon.
Pepto bismol should not be given to vomiting dogs since it contains salicylates (the active ingredient in Aspirin) which can irritate the stomach which might worsen the situation.
3. I'd also start her on a good quality, canine probiotic such as Forti Flora or Resources Protegrity GI. Again, I'm not certain what is available in the UK but more than likely your local pet or grain store will carry them. These products can be extremely useful for gastrointestinal issues (and to help strengthen the immune system as well).
4. Encourage her to drink often to keep her from getting dehydrated although this is a concern when the dogs are older than she is. You can also offer her Pedialyte (hopefully, available there) which can help to replace electrolytes lost in the looser stools.
Hopefully, the above will be sufficient to get things under control but if not (and if she hasn't worsened in any way), then a vet visit next week may be in order....which is what I think you planned on doing anyway.
I hope this helps. Deb