New Rescue Pup - Nervous!

I have two senior dogs and recently adopted a rescue pup (8 months old). Her trauma and fear seem to be more extensive than we were led to believe. I do not know her entire story, other than she spent at least her first several months of life in a puppy mill. She was in foster before coming to us. We are only on week two, so I know about the 3-3-3 rule & this is not a complaint about her! I just want to help her succeed. My own anxiety is through the roof, to the point where I've lost weight, missed work, etc. because I have a deep empathy for and genuinely want to support her. I am also juggling two young children (both under 6), work, school, and chronic (not terminal) illness.

We are working with our vet and not medicating at this point (he wanted us to try calming chews, CBD, or benadryl - I do not plan on giving Benadryl). We also have an adaptil collar on her. We have hired a fear-free certified trainer to start this week - not for obedience, simply to help us help her gain confidence.

I have an overwhelming amount of guilt that we are not the right household for her. She doesn't seem to have separation anxiety necessarily, but she is very fearful of humans. Her coat requires frequent brushing and we have not been able to do that. She is not aggressive...she just appears to shut down/freeze more than anything. She has made immense progress in two weeks. She will follow me room to room and observe. She is learning a lot from the other dogs. We were told she was crate trained, but the transition into the crate is traumatizing for her (and her humans), so we have honestly been avoiding it at this point. We do work and leave the house for outings occasionally, so we need to be able to safely confine her. She is potty trained, but getting her to go outside requires a very specific routine and she will not walk with a leash. We have been using enrichment items like frozen kongs, etc.

We have a vacation coming up in a few weeks. I told the rescue about this prior to adopting because I was worried we wouldn't have enough time. I can't cancel our trip, my kids would be devastated. The foster offered to watch her during this time (in her home) and I feel that might be best? I don't think there is a perfect answer..I just fear that a stranger (even if they met several times prior) might be worse.