not sure if 'transition' means 'meet the person you're replacing and get an overview, find the break room, etc' or 'training'. it's a little odd but not totally wrong if it's the former, but if it's the latter, it's definitely not common.
if she just wants you to come in and get the lay of the land, it may be a courtesy to both of you and you might not get paid. but if she expects you to come in for a day of training, of course you should be paid.
since you have a current job, it's sort of a moot point, isn't it? you can just say to her, 'i'm sorry, i've committed to finishing out my two weeks' notice at my current job and it would be unethical for me to take off. is this something i can run over and do after i finish up work at my current place of employment? no? i look forward to seeing you on my start date.'
khairete
S.