majorspannermonkey,
Good question...
Firstly, just to clarify, your fiance is not based at Heathrow. She is based in London. Which means she will be rostered flights usually only out of Heathrow and Gatwick. Juniors get quite an equal split of flights from Gatwick and Heathrow.
When she is promoted to Senior she will get mainly flights from Heathrow due to the fact that there are less seniors on Gatwick flights.
She can expect to work every Xmas and New Yr until she has enough seniorty within her rank to successfully bid for the time off. (Probably around
3 yrs).
Weekend flights are not rostered to junior crew members. Some months she will work every weekend, some months some of them, and occasionally she might get them all off! It is random (tho I agree it doesnt always seem like it).
Im sure her roster is not inaccurate, and just to let you both know, commuting to and from work at her base (London) is not counted in her accountable "work hours". The crew bus does run to a scheduled journey time of 1 hour 10 mins, and almost always that is correct (traffic permitting of course!)
I hope thats cleared up some of your concerns...
VB