Well, I'm no expert..but if it were me, I would keep it 45 mins to an hour...and make sure you are not neglecting any areas...arms, core, legs...maybe use the total workout as a template for how much time she spends on each area? If you could do cardio on top of that without burning out, that would be a bonus.
I think the basic workout plus is the reproduction of the one that came with the VHS tapes that I have..I believe it was called Mini Max and was 15 mins..it included the primary back stretch and some other moves--I remember that makes a good starter add-on to make your workout more complete. I think I did a bootcamp once with that plus Hit the Floor.
It's been awhile since I have done any T-Tapp. I need to search my house for that lower body DVD (Tempo Lower Body..I think it is called?)..I think i was intimidated by it when I bought it, but I'd love to try it now.
Which of hers do you have? I'd like to try some of her newer content but they are so expensive.