sorry to be an a$$hole, but shouldn't you have asked all this before you signed up...?
It doesn't help much, but service life is pretty unpredictable and dependent on world events. Any promises you make based on this advice can be completely changed by elements out of your control. Equally, it massively depends on which stream of flying you end up at..
But,... that said, typically, tours are 3 years long, 5 years sometimes in 2 Group. The training process is long and involves several short courses at different locations. Typically, fast jet stream:
1month Cranwell, groundschool
8 months Cranwell/Wittering/Wyton Elementary Flying Training
10 months Linton on Ouse Basic Fast Jet Training
18months Valley, Advanced Fast Jet training, and Weapons training
You could then be posted to rural Lincolnshire or Northern Scotland, or anywhere in between. Between the stated courses there are likely to be holding jobs at other locations of indeterminate length. This will invariably involve moving again.
Otherwise, there will be professional and officer development courses held from 1 week to 4 weeks at other locations like Shrivenham, Cranwell, Northolt, Henlow....etc.
How long on operations overseas....? Hah, no answer here my friend, ask 2 different pilots, get 2 different answers. Tornado F3, almost never deployed, apart from occasional Falklands det, vs Puma Force, almost never at home, 6 month tours in Iraq and Afghanistan with 6 months at home in between if you're lucky.
Scope for working long term overseas is now fairly small and limited to a very small number of specific trades/branches. That said there are opportunities. Embassy work much scaled back and most DA jobs are Wing Commmander or Group Captain level so expect them very far down the line if at all.
I don't mean to be negative, all this change and variation is actually one of the things that attracted me to the forces and makes life interesting. But it can soon become tedious if you are being given hell for it at home. If she's not up for all this upheaval and operating a singly for most of the year while you are away, then my friend you/her have some difficult decisions to make....Good luck.