Personally I don't like flipping a preggo female rat upside down by the tail. It suddenly shifts a load of pinks around and would press a swollen uterus upwards towards her vital organs.

Instead you can just as easily grasp her under the front legs (armpits sort of) and dangle her gently for a moment with her hind feet just touching your other palm. If she's preggo and starting to show it, she should look like a nice fat pear.

The rat looks pregnant to me but she seems to have the body shape of a fairly young female. What was her weight prior to breeding?