I have a pair and think they're a good boot, but the most important thing to determine if your sister will like them is if they fit her feet well.
As for the FT lacing, I rotate my foot at the ankle, in both directions, while tightening (pulling up) on the inner lace tab. I find that gets the ankle area nice and snug. Then slide the tab down to lock it in. You'll figure it out.
Then for the outer laces, I pull the outside lace tab first, flex forward at the ankle a bit, straighten, then do the inside tab the same way.