"She has one little bread."
that would sound like "she has a lonely little bread" though i think seul would go after pain
I'm not sure if your use of 'seul' in the sentence is grammatically correct but in any case, the word 'seul' means 'alone' or 'only', and in the sentence it is simply 'one'. Indeed "she has only one little bread" and "she has one little bread" convey the same facts about how much bread she has but they are different sentences with subtly different meanings and different French translations.
I think that a closer translation of that would be "She has but one little bread"
It's just not a sensible English sentence. We might say "She has one little piece of bread", or "She has one little bread roll" or "...one little lice of bread". It must be difficult for those learning who don't speak English already when things are presented into this odd way.
In starbucks, they sell regular scones, and petit scones. so I think we do, it just depends on the food. I could say I will take a small bowl of rice. or a small rice. a large steak. etc.
This is a good overview: http://french.about.com/od/grammar/a/adjectives_4.htm
This would be like saying she has a small amount of bread. "Un petit pain" is the term for a dinner roll. Notice the adjective "petit" describes the bread itself, the bread is small, not the amount of bread she has. If you say Elle "a un peu", you said, she has a little quantity of bread. This may seem unimportant, until you need to say "Elle a 20 petits pains" that's a lot of small breads!
does little bread translate to "baguette," or is that only for little roll?
I do not think so, a baguette is very long. Though a baguette is also referred to as Pain Long I think they make petit baguette (google that and you will find images) but I think they are called petit baguette not petit pain. I think there is a difference. As a baguette is stick shaped. I am going to Paris in a few weeks I will ask a bakery.