Pardon my mistake with writing Avios instead of Tier Points. So, it seems she will have enough BA sectors by the end of the summer (7 or 8) and then with the 4 long haul sectors in Premium Economy she will get 360 TPs. So, it seems she will be silver again by the time she reaches LHR on her return to DXB - and maybe sooner if she gets some extra TPs from her (hopefully upgraded) CX flight sectors.
Thanks to all for this advice/info.