I hope there is nothing bad being said.. lol ... Couple things to go on there -

First when it comes to open office they have limitations on nesting as well as limited formula functions. So this is going to happen the more complex we make that sheet.

Freezing, I would simply highlight all the rows from row 1 down to right before the row you wish to freeze (The headers of the columns so 1:21) and then group it via the data tab.
This will allow you to collapse that section while you don't want to see it. Then freeze it how she was wishing to do there.

The Active Inactive is only important when it comes to the totals. It groups the sums based on what she indicates there. The drop down in C for the monthly breakdown will also be utilizing that column so again it only affects the totals.

I believe that is it and you should be good!

Thanks