The first thing to remember is a contract of employment is only enforceable if it complies with employment contract law. The same applies to Conditions of Employment. You cannot state that an employee gives a weeks notice - if the law says otherwise - and in this case (from what you have said) it does!
For this reason it is critical that you get the amount of time she worked for you right, because the law says that neither the employer nor the employee has to give any notice if they have worked for you for less than a month. You are saying it is 4 weeks - so it is very close. After a month, 1 weeks notice must be given by either party.
The easiest way to look at it is take to the actual date she started - say 20th September - one month would be if she worked up until yesterday - 19th October.
Either way, you cannot legally transfer a debt of not giving notice over to witholding holiday pay. You would be breaking the law. If you want recompense for your trouble, you will need to haul her through the civil court!
Now that the annual holiday entitlement is 24 days, she has accrued up to 2 days in the time she was with you. To find out the exact amount, use the tool posted in 'Holiday Pay Tool' on here.
Now, you say she has already taken 2 days holidays, if you did not pay her for these, they are classed as unpaid absences and she still has to be paid holiday pay. If you did, then she has no holiday entitlement remaining, so there is no problem there. You may even find that she hadn't accrued a full 2 days. In this case, work out the holiday entitlement in hours and the hours she actually took off and then can you legally deduct the difference from her final pay.
Finally, you should know that the actual amount of money you give as holiday pay can be worked out as an average of the hours she worked in those four weeks. If she had two days absence, this will work out in your favour. For example: Lets say your employee is full-time and works 8 hours per day. She did 40 hours in the first week, had a day off in the second week - 32 hours, another 40 in the third, another day off in the fourth - 32. That's a total of 144 hours in 20 days, so the average is 7.2 hours per day. Now lets say she did accrue exactly 2 days holiday pay (to keep it simple) you only have to pay her for 7.2 hours for each day, instead of the normal 8.
Adjust this to suit your exact situation.
(EDIT)
I have made some assumptions here and tried them out on the calculator:
Your employee started with you on 24th September and you got the text yesterday 19th October - so she worked for exactly 4 weeks - no notice required by law.
Her holiday entitlement works out to 1.6 days.
So in the above example, you only have to pay her a total of 12.8 holiday hours partly because of the 16 she actually took off as unpaid. So you can legally deduct 3.2 hours from her holiday entitlement in her final wages.
Now simply pay her for the hours she has done, and forget about it. Concentrate on getting another cleaner - quick!
