Mmmmmm... That's quite a dilemma. Must resist voice inside that makes me tell you to tie her up with every single thing you have and keep her for two months...
Just kidding. Seriously now, this kinda depends on how you got her to agree. If it was through months of nagging it would be completely different than, say, a bet you both agreed on, or better yet, was her suggestion. For the most part I think you can use almost any reasonable amount of rope or tape. If you choose not to gag her you'll know by the tone of her voice when she just begs as play and when she's really serious. On the other hand, a gag almost doubles, if not triples the helplessness of the situation. Again all depending on how much she wants this. In any case, I would not suggest tickling longer than twenty minutes or leaving her tied up for over an hour. If whe you release her she wants to stay tied it is sape to say 'grats on the new TUG buddy"
btw, all sentences above are mere opinions.