It is very difficult, can try replenishing often, to make it more appealing, sprinkling something yummy on top (dried herbs, etc), cutting down on pellets (can’t remember if you feed any?)
I don’t see any benefit to activated charcoal as it doesn’t work in that way, but I am not an expert and it’s up to you what you want to try.
With “bad” bacteria proliferation it is the gas production that is the issue rather than the toxins produced, usually.
The only pre- and pro-biotics I have seen were sold by the Vets, so maybe you could give it a google to see if there is another source?
Clostridium proliferation is unlikely, it is usually only a result of high doses of certain antibiotics, and if serious is usually accompanied by severe diarrhoea. How are her faeces?
I wouldn’t suggest using products cross-species, and as it is an antibiotic treatment waiting one day won’t make a huge difference.