Also t Tia may not be in her natural form ..the voodoo lady could all be a disguise hiding who she really is..Calypso. So she could have still made that deal with Beckett..
here are some thing that make me think she and beckett have spoken and are prompting along a Jack/Liz relationship so that a Will/Davy thing can happen
1. Beckett knows about the magical compass..which we later learn Tia gave to Jack. So she has all the info on it..and Beckett suddenly does too when we meet him.
2. He says to liz that the wedding being stopped might be "FATE INTEVENING" hint hint he stopped the wedding so that this Will/Davy fate could happen.
3. He hints to her that she likes Jack (prompting along the relationship)
4. The man working for Beckett...was he REALLY there at the beginning to grab Liz and put her back in the cell..or was he there to make SURE she didn't end up where her FATHER was planning for her to go(away from Will and Jack). I say this because later..he sees her in Tortuga and does NOTHING to stop her going off with Jack..He goes back to Beckett and tells him that she has gone with him..letting Becket know that everything is going to plan maybe?..if not why not grab her right there in Tortuga?