Are you planning to breed your little girl? If not, please get her spayed as soon as possible. We lost a dog to pyometra years ago. If I sound like a broken record, there's a reason. It was a very horrible thing that my family went through and it all could have been avoided if we had gotten her spayed.
http://www.marvistavet.com/html/body_pyometra.html
The yellow foam she is vomiting sounds like bile from an empty stomach. Do you free feed her to stick to regular mealtimes?