I'm not sure what you could get that would cheer her up - chocolates and squishy pillows were enough for me, but I didn't suffer from baby blues.
If you live near her you could print her out a set of tokens, redeemable for a couple hours of babysitting/house help from you. Babies are a lot of work and most new mums would kill for a couple hours off to nap or relax while someone else takes care of Baby or does jobs that she'd be too tired to do. That might not help her cheer up while the baby is in the hospital still, but she'll certainly apprecciate the gesture.
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