I've read this whole thread since was confused by the time span between the first post and the present. If your older White's is close to 3 years old; it should be full grown and at 2.5 in. (is that snout to vent?) long appears is a bit stunted.

If accurate; think 0.5 in. SVL difference between them is not so great that the smaller one looks like a meal to the larger one. Like Gail stated; this is the first time I read about White's fighting for dominance. Maybe your older frog has lived alone for a long time and does not want to share it's enclosure. Every animal is different and there is always the exception to every rule.

Recommend get either an ExoTerra Medium X-tall or Large X-tall enclosure and set it up to your desires (either with artificial or live plants). Then once enclosure is ready; introduce both frogs at the same time to their new home. Since both frogs are new to that enclosure, they will not defend it as their territory. Also, by going with a 36 in. height X-tall enclosure, the White's will be less stressed out about space and need to guard it from other frogs. Good luck !