I think that you shouldn't confuse getting some sort of relationship back with your daughter with getting her out of the Watchtower.
Personally I'd think that the former is a better and more realistic possibility.
She needs to feel totally unthreatened by you.
How long did it take for her to reply to your gift? I'd wait approximately the same amount of time and then write back.
I would ignore any mention of religious stuff totally and focus in a gentle, natural way on her and your relationship - not too gushing and definitely no bargaining or pleading (however mild). I would leave the letter on an open positive note, nothing that requires an immediate response, maybe just a simple "take care and catch you soon"
I would then leave it.
In a couple of months or so (if you haven't heard anything) send them something again - a card, postcard etc.
Don't acknowledge or mention anything about The Watchtower or religion at all.
If you can manage to get through half a dozen exchanges of correspondance or manage to communicate for a reasonable amount of time (it could be a year or more) without any mention of WT stuff, she may start to relax and trust you. In it is quite likely that she'll be puzzled. Eventually she will probably ask you something directly. At this point I would suggest that you totally deflect it by saying something like "You know, I really love you and respect your views and I don't want to discuss anything that will make you think otherwise" and refuse to be drawn further.
By doing this I believe that you have a chance of rebuilding - in time . . .
Rushing or having an agenda of your own could be disasterous.
I'd forget Steve Hassan's book at the mo and ask yourself which you want more - a relationship with your daughter or the possibility of her batoning down against your approaches.
Pub