Hello Marilyn my name is ***** ***** I will help you.
The Border Control will want to make sure you are a genuine tourist. Therefore if you can show that you have stayed for previous years and that evidence your mum is ill, there should be no issue.
The test is just are you a genuine tourist and if so, do you intend to return home at the end of your stay.
If you satisfy that test it is not an issue.
The 6 month rule does not apply for less than 6 months, but of course if you come over and keep going back and forth that may raise an issue.
Once will be fine, maybe even twice.
Can I clarify anything for you about this today please?Alex