It will be busier.
When I was pregnant with my 2nd child, I did this: INCORPORATE my Daughter into 'my' pregnancy. I made it a "we" thing, instead of a "me" thing. Meaning, I spent a ton of time, acclimating her to it, to her baby brother in my tummy etc. I even took her to my prenatal visits, which my Doc, encouraged. He even taught her how to use the Doppler heart monitor on my tummy. She loved it. I, each month, explained to her the pregnant "phases" Mommy will go through: ie: my tummy gets bigger as her baby brother grows, I will get tired, I will not be able to carry her or do running around sometimes, I will need to nap etc. And we would nap, together.
And she understood like a Champ. AND, this also helped her in BONDING with her baby brother already, even if he was just in my tummy. SO that, once he came home from the hospital, she was not all shocked about it and really loved her brother already.
We took pictures of HER each month, with my growing belly, she sang to her baby brother in my tummy, she rubbed my tummy and would just talk to her, baby brother.
Then, once baby brother was born... I explained to her, EACH month, how he is growing and changing. The "phases" of a baby. I also explained BEFORE baby came home, what a baby 'does.' ie: it wakes a lot, it cries, I nurse him... just like she did and I did for her.
I explained a baby cannot do what she does etc.
I ALSO explained to her, that I respect HER things. I DO NOT EVER, just 'expect' her to share EVERYTHING with her brother, and that I know her things are special to her. A little child needs to know that.
I also explained, that just because she will be an 'older' sibling, that does not mean, SHE has to be all grown up. I know she is a little child herself. And that she can tell me anything, her feelings, worries, upsets etc., and I am there for her.
That she is STILL.... "my first baby."
All of this, made a good transition for her. She LOVED her baby brother even while still in my tummy, and she had no jealousy.
I never expected her to be any 'different' just because she was an older sibling. I also told her that, she will NOT be used as an 'example' for her little brother. She is herself.
I told her also, I will never expect her to be 'perfect.' She has her developmental phases too. Its okay.
My daughter, was also 3-3.5 years old, when I was pregnant with my 2nd child.
all the best,
Susan