How do i know if my dauchshund is pregnant?

We know she bred with a dog that stayed at our house for about a week(it wouldn't leave! my dog, bella, got loose. it was a stray and presumably had never been fixed). This was about two days ago. What signs should I look for to know whether or not she is pregnant? if she is, should i change her diet? Anything I should know? if it makes any difference, she is a miniature.