I am trying to complete her P14 and I thought it would be category A but it won't allow me to have a zero in the LEL box but she has only been working there for a few weeks
NI Category X is used when there is no NI liability. If the worker is earning under the LEL (£107 per week for this last tax year) then there will be no NI liability. Even though my software tells me that I should use category A for a certain worker, when I call up the end of year P14 it changes the letter A to a letter X and there are zeros in all the boxes.
Category X is where there is no liability to NI. Most obvious example is where you have someone who has reached retirement age.
£146 is above LEL so I would use category A
The op said that the employee was earning less than £146 per week. I suppose it depends on how much less. If she earns £107 a week then the software uses Cat A NI, but if she earns £106 a week the software changes it to Cat X.