My 82 year old mum wears maxi pads (1.5L) at night but is pulling the pads aside (to scratch) and wetting the bed, what can be done?

I used Peapod Mats for Luz. worked great. Washable. I even used them on the floor where necessary.
This was in addition to her protective under wear.

I have purchased a pack of 4 large quilted waterproof incontinence pads (34"x52") to place under my husband at night. They are super absorbent. When he has had an accident, I have never had to change the sheets. Just remove the pad and launder. That being said, he needs more than a pad. He wears incontinence disposable underwear as well. (I prefer the Walmart brand) And if he has had liquid in the eve, I add an extra "guard" inside the disposable.
And I agree with GardenArtist. Find the cause of the scratching. If it continues, she could develop sores which creates an entirely new set of problems.

I would address the reason for scratching. Is her skin dry? Does she have a gynecologist you could ask?

Have you tried Depends(the pull up waterproof underwear) or even an adult diaper for her? Sounds like she needs more than just a maxi pad at this point. She wouldn't be able to remove the Depends brand and it would certainly keep her and the bed more dry. Also make sure she has several waterproof pads underneath her when she's in the bed or even sitting in a chair, that way if it does leak, the pads will get the brunt of it and not the mattress or furniture. You can also reinforce the Depends with a maxi pad if needed just for reinforcement. I actually had to do that with my husband, before he got his supra pubic catheter. Hope that info helps. Best Wishes.