Breast milk question ?

Baby is 4 months old and has been refusing the bottle 90 percent of the time. We stopped for a while and tried to reintroduce it to her. She took it twice last week but refused the last 3 attempts she prefers to drink it straight from the breast.

My question is say for instance I pump and s/o offers it to her immediately after I pump

If the bottle goes in her mouth and she refuses. How long is it good outside for and can it be reheated for later.

I remember I read something about bacteria getting in the bottle once they put their mouth on it making it not last as long as it would outside