It does take a while for it to settle down, and during this time I found my spectacles didn't work well- reading was difficult and I wasn't able to drive confidently - because, of course, the prescription in the first eye I had done was wildly different from before. And then, when the second one was done a few weeks later, there was a total period of four months before I could get a new prescription from the optician. You just have to be prepared for the total process to take about 6 months from the time the first eye is operated on, assuming the second eye is to be done a couple of months later, because as with any operation on a delicate part of the body, it has to have time to heal and for the eyeball to return to its normal shape. If you get your new prescription too soon, it would need changing again within a very short time. The prescription which was right for me at first needed changing a year later, once both eyes had fully settled down, so you have to be prepared for this as well. Also at first your brain needs to re-train to the new arrangements, like when you have a new prescription normally, as it has to get used to the new way of seeing.
I was glad to have had it done for another reason - because of the 6-monthly checkups I was offered, I was diagnosed with early-stage normal pressure glaucoma, which has no obvious symptoms or sight impairments until it's well advanced. If I hadn't had my cataracts fixed, i wouldn't have had the specialist eye examinations which diagnosed this, so i'm grateful now to be on eye drops to slow or halt the progress of the glaucoma, plus regular tests to see how it's getting on. The type of pressure test used by an optician to diagnose glaucoma isn't sensitive enough to detect normal-pressure glaucoma, because as the name suggests, it's not due to high pressure within the eye, but to damage to the optic nerve itself.
I do hope your Mum will get on OK, - just keep on using the prescribed drops, that's very important to help with the healing. Yes I agree with Margaid about the possibility of allergy to drops containing preservative. The ones I had for glaucoma made my eyes really sore, but now i have the same drug in a prescription with no preservative. It comes in little dispensers holding a single dose, instead of in a bottle, so it's guaranteed sterile on application.