P.M.
I doubt that she's got much sense of what "will" change, but you have almost certainly become tireder, more distracted, busy preparing space for the new baby by now, so things probably are changing. Children pick up all sorts of body language and moods long before they have words to describe them. If they don't understand the source of these feelings, they can and do morph into vague anxiety or neediness.
It's also common for separation anxiety to set in somewhere between 9 months and two years (or even later when any major change happens, such as a parent's illness or divorce, a move, or starting school).
If you haven't yet, it's time to tell her that a new baby is coming. Tell her how important it will be for her to to be your helper. Make extra efforts to let her know she will always be precious to you. There are also many good books for children of various age levels to help them look forward to a new baby.
Congrats on your expanding family. I hope all goes smoothly.