I don't think my "new" dog has had a BM for 3 days!?

She is a new to me 2-3 year old 80lbs mutt. We have had her for slightly more than a month to keep my 75lbs Plott hound company while the kids are in school and my fiance and I are at work. She has been a great addition with the exception of being a garbage eater. She was rescued half starved from a hoarder and probably only ate garbage for most of her life. We do our best to keep everything locked up but we have slipped on more than 1 occassion. My fiance or I let both dogs out and usually watch for them to do their "business" and then let them in just until she is trained to stay out of the garden and prevent any more squirrel slayings (from the hound not her). I have not seen her have a BM in several days. She is not showing any discomfort or any signs of slowing down including playing with our 4 kids and the hound most of the day today. But I did find a pile of dog vomit (but I don't know from which dog). It is possible she may have gone and I just didn't notice and neither did my fiance. But I am worried she may have eaten something we don't know about and I don't want her to get ill. And, I am hoping to avoid vet bills as we are still paying off our last dog's cancer treatments. Am I just being a paranoid momma here since she does not appear ill or should I bite the bullet and call in the professionals?

I think you need to consult with your vet. Even though you said she doesn't seem to be having discomfort, I still wonder if maybe she could have a blockage. If you are concerned about expense, talk to your vet by phone. I'm sure that your vet will be able to tell you if you need to bring the dog in. Good luck.