I totally agree with Slash we had 5 staff at one point and got have been put off taking people on for a while, its not to be taken lightly. You must have all procedures in place before taking on staff, looks like you've just taken a cleaner on, without thinking about quite a few things.
If she already has a job, you will have to pay her tax & NI on top of her £6, which you wouldn't have to do if she didn't have another job and only worked part-time.
Have you told her how many days holiday she will be getting, procedures for sickness, disciplinary procedures. It's not easy to get rid of her if your not happy with her work.
Good Luck!