Normal
Really depends on how often you want to transfer her. Phormictopus are fast growers. Being opportunistic burrowers, there is no such thing as an enclosure that is too big (not saying too high) as they will spend most of their time in the burrow. So if you don't want to deal with transferring as often, I would go bigger. Either way would work though if you don't currently have space or budget. Gorgeous spider BTW.