On a family sim you'll need to call BT for the PAC, you would lose any multi sim discount on yours though.
If it's more data needed, you could also look at a new plan for your wife and remain with BT, might as well look at your usage as well, get both plans how you need them for your usage.
Another option if you have BT broadband, look at how much an upgrade to Halo will cost, the Halo broadband packages will double any data you currently have without needing to change the mobile plan.
