The amount you are relying on is your ANNUAL salary, so you want your employment letter to state your total annual salary - not your salary for six months.

For example, "Bob has been a permanent employee of xx company since June 1, 2015. His current salary is £25,000 base per annum (plus overtime and shift differentials) as of January 1, 2017. Prior to this, he was earning £24,000 base per annum." Something like that.
Are you salaried or non-salaried?
You'll use Category A, as you've been with the same employer for longer than 6 months. Category B is if you've changed employers.
Honestly, I don't think she can switch back to the 5 year path after having been placed on the 10 year path. But she needs to do her renewal regardless, so you'll still want to provide all the documentation. Ksand or Sirius, do you know if you can switch back?