Going 2 have a new stepmom?

ok my parents got a divorce and my dad gets full custody of me and my mom gets my brother. i dont think i will rarley get to see my real mom again. the problem is i dont no if i feel comfterable talking to this lady about things like going to the store to buy me tampons and other femminme things. how will i talk to her about this stuff. my dad and her are engagegd. im very nervouse, i havnt brought it up to her. how could i start the conversation?