At similar ages, DD and Pandora's DS had a weekend together - and we spent all weekend keeping them apart! It was pretty ordinary for all of us really. Two seconds alone and there were tears (DD wouldn't fight back if being pushed etc). about 3 months later they had a few hours together at Div's, and then another couple of months later, we had another weekend together - and the change that came about over the latter two visits was huge. they were the best of friends for the whole weekend

if it were me, i'd give it a bit more time and then try again. 16month olds aren't going to learn the difference between gentle and rough - she will just end up distressed and reluctant to be around this child longer term