Heavy
As a MIL it took me a short while to understand that my son and daughter-in-law had a life to establish as a couple and that my life and theirs ran along completely different dynamics.
Unless your MIL understands that your life, both as a couple and as individuals, does not revolve around her emotional needs, it is going to be a problem.
All you can do is stick to the boundaries you have put in place and gently explain that you have a busy life of your own to lead. You can assure her of your affection, and re-assure her that if you don't communicate as often as she'd like, it is not because you don't care, but because you are simply very busy preparing for the new baby (
congratulations!).
When an individual is emotionally dependent on another, it is a huge problem -regardless of the relationship between them. You will need a lot of patience. But stick with those boundaries otherwise you will be emotionally 'blackmailed' and the resentment will boil over.
Generally speaking, when our adult children get married and start a life of their own, we should already be leading our own lives; either still working or in retirement. I can only assume that your MIL is emotionally dependent on you because she maybe doesn't have a very fulfilling life of her own? Of course, you can't say too much on a public forum but, if that is the case, at least you will understand the reason for the intensity of her dependence on you.
All I can suggest is that you be very careful in your choice of words when communicating with her, establish a routine when the baby arrives, be as kind as you can under the circumstances. Other than that there's not much else you can do. But you are not responsible for her emotional needs.