My dog seems so sad, what could be wrong?

Here is a brief explanation of her current cirstances. She is my dog, but always lived with my mom & brother (a much busier house). She has been at my new house for almost a week. Did good at first and better behaved everyday as far as whining at night, roaming around lost-like, etc. But today she seems SO sad. Her little eyes are sad. We recently found out we will not be able to keep her in our new house :( So I am in the process of interviewing families to find her a new home. Yesterday we visited a house with a male dog same breed and they got along great. I had read once some where on this site that many dogs get sad after having played with another dog. Is there any truth to this? It's either that or she misses her first home, my mom's house. But it has ONLY been today that she seems sad & she has been here almost a week. OR is it possible that she can sense my heartache and stress at the fact of having to re-home her?!? or absolutely not? Otherwise she is eating & drinking fine. Opinion appreciated