I see your dilemma.
With the T25 you have the length x width thing covered and you've got room to have a shelf installed for added square footage. However, you're reaching in 30" to clean with only 16" of "head room."
The T20 offers that extra height and still have the shelf installed but you sacrifice the extra depth (floor space).
Soley guessing on Suriname adult length, I'd go T25 as to not have her grow out of the T20.
The T25 is also "sale" item and who doesn't like a sale LOL