H.G.
Don't worry about your kiddo leaning on your bump! As long as she's not kicking or hitting you, your baby is well protected. :) It's bonding time for them, anyways! You can keep her from climbing on your belly, by taking her hands and having her "pet" or gently pat the new baby while you cuddle.
Can you get a small stepping stool, to help her get into her high chair? I bet she'd love that! Plus, then you can just give her a boost in, rather than doing the full lift.
But honestly, if you're having a healthy pregnancy, it should be ok to lift her into her car seat, etc. Just be careful, and snuggle on the couch as much as possible so she doesn't notice that you don't pick her up as much. And use your legs, when lifting!
Good luck with that new baby!