Have her come round and have a look at your house so she can tell you how long she would think it would take each week. Make three lists to go over with her when you chat to her: jobs you want done every time she comes, jobs you want done occasionally (once a week/month, when there's extra time, etc.), and things you don't want/need her to do.
For example, I don't have ours change our bedsheets, but she does make the beds. She cleans the oven, cleans behind the bedside tables, chests of drawers, etc., once a month. She doesn't put dishes away, but will wash them if there are any left in the sink. She doesn't take the rubbish out, but will empty the bins, etc. just because that's my personal preference.
After her first few visits, you'll probably think of things that you'll want to either add or remove from her job list, so just communicate with her, and it'll be fine!
Enjoy your spare time :)