Test.Test.Test

The mini Hydrometers that do temps and RH have a variability, if you read the box it came in it will say something like +/- 1.5c or something along that line, meaning it can by off but as much as 1.5 in either direction. Eg, if its really 10c. it could read +11.5 or -8.5, they are not the most robust tools, I would trust the other thermometer more so. And it also has a variability but its likely more finely tuned and accurate. Not a drastic difference, should be fine for monitoring temps. Now if temps are hitting 15c at night its a bit cold, it will slow the rate of things happening and around 10c it degrades somethings in the plants and they start to get fall colours. Ideally it should not be fluctuation more then 8-10c between day and night time temps. if you running 30c days and 20c nights that's ok. the lower the chnage the better but I never care to try and fix that to much. I let my tent get down to around 18c at night and it will hit 29c in the day.

You can do both at the same time but know that both are going effect the plant. I suggest doing them separately to allow a little bit of recovery time for your girl. She looks like she will be fine in that pot for a couple of weeks. I suggest topping her and then transplant. You can also use Mycorrhizal fungi root treatments to help with the transplanting process.