As long as you stick to your plan of waiting til she's big enough to upgrade the added height won't hurt. Some say their BPs will climb if branches are offered, but in my experience, none of mine have ever been climbers.
The added height will require a bit more to heat the enclosure, but as long as you adjust your heating equipment accordingly it'll be fine.
Some will probably say the added height is a waste of space for a terrestrial species, but it's all in how you view it.