Firstly is she anaphylactic? if so she will need to speak to her GP before coming over as the kittens could be very dangerous to her.

this is all from my personal experience with my father's allergies.
she can get a special allergy medication from her GP. I take Telfast and it works brill with my mite, mold, rabbit and straw/hay allergies. Also bathing the cat once a month or so with a teatree bath for cats will help with the dander. but be very careful bathing kittens as they can get chilled very easily. try not to blow dry them as it will increase the saliva dander. vacuuming the house and dusting regularly before your mum comes over and also keeping some hand wash for her to wash her hand if she touches them. Explain to her not to pet the cat and then wash her hands and try not to touch her face. you can also open a window before she comes round. cat allergies are generally contact dermo problems so she would need to touch the cat. any other allergy meds (piriton, zirtek, benadryl) should help with the non contact stuffies!

here is some info on Anaphylaxis - Wikipedia, the free encyclopedia i only asked if you knew if your mum was anaphylactic as it's very serious and my advice wouldn't suit her if she was. I didn't want to assume she wasn't and have you take the advice and put her in danger as you didn't specify. I wasn't intending on scaring you If your mum was anaphylactic she would know and would have the proper meds for it. but i couldn't assume that she would have told you that she was so i asked. OK? sorry for the confusion.