Thanks for your query.
as mentioned by you your daughter has fallen and there is hematoma
formation on back.you have also mentioned that swelling is now decreasing in size.she is active as well which are all good signs.you need not to worry,
I advise you to give her paracetamol
for pain.and monitor her for 24 hours for any warning sign like vomiting
.any altered behavior.any bleed from ear or nose.and in case you find any then take her to doctor.
Your daughter will be fine.