Assume your new foster dog will have accidents in the home, even if housetrained; the stress and new boundaries in a new home with new people … it’s a lot for a dog to understand.
Take your dog out on a long leash at 2-3 hour intervals to the area designated as the bathroom. Allow her to explore and get used to the area. When she poops or pees, praise like crazy, and then reward her with a few minutes of play, sniffing or a walk; sometimes food treats are helpful for a dog who is “treat motivated”.
You can associate pottying outside with a word (do your business, go pee, etc) but please make sure all members of the household use the SAME word so the dog does not get confused.
When inside the home, for the first few days, keep the dog within your line of sight; close the doors to other rooms in the house and/or crate the dog frequently when unsupervised and to also accomplish the need of “crate training”.
The dog should be kept near you in the house so that if she begins to potty inside or looks like she is about to, you can break her focus (say “nahahah”) and take her out immediately. Punishing a dog after the fact is ineffective and confusing to the animal.
Never push a dog’s face in her excrement or urine.