When do she transfer her number over??
If it was within the last week or two then check the sim carefully as giffgaff now send out a three in one sim (www.is.gd/triosims)
Otherwise she should go to www.giffgaff.com/orders/mgm
and order a trio sim.
When it arrives do this:
1) Log out of giffgaff,
2) Go to www.giffgaff.com/activate
3) Enter 6 digit activation code
4) On next page choose the "I already have an account" option and log in
5) Confirm you want to perform a sim swap
6) Confirm a second time
will appear but with her phone number missing. When you refresh the page and her number reappears then the swap is complete.
Sim swap transfers:
From one sim to another.