I've been going through a similar situation trying to find something for my wife. It's become much more complicated than I would have ever thought.
At first I wanted to give her something purely for self defense because I never thought she would ever use a knife for EDC purposes. I wanted a fixed blade so that she wouldn't have to deal with deploying a folding knife under stress. We went to the local Army Navy and took a look at the Smith & Wesson HRT Badge knife, this is one of those bear claw neck knives. I figure this is ideal because it would be difficult to disarm her with that finger hole and the serrated bear claw could do some real damage if it came down to it. Well it would be perfect except for the fact that she could not remove the knife from the sheath to save her life. Whether it was lack of coordination of pushing the plastic and sliding the knife out, I don't know but she just could not do it. I was concerned.
We went home and she decided that she just might use a knife for everyday purposes so I started to switch gears and think EDC.
First off, anything with a spydie hole seems to be a problem for her to open one-handed because of her thumbnail - it's significantly longer than mine. Forget about flicking open any Spyderco. I thought the Delica was a perfect size and she loves the look of the Dragonfly Tattoo but after watching her fiddle around with my Spydercos, I was convinced she should not be carrying anything with a spydie hole; I cringed watching her fiddle with the lockback.
Secondly, thumbstuds also pose a problem because of forementioned thumbnails...?! I gave her my SOG Aegis to try..I've never seen an assisted opening folder open so slowly before in my life. I assume the thumbnail is dragging on the blade as it opens.
I have since resigned myself to the fact that she will never be able to quickly deploy any folding knife so I don't care about that aspect any more. I just figured something simple and small should be fine so I ordered one of those CRKT Shrimp knives (McGinnis design) to surprise her; they look cute and are small but useful. She loved it except for the fact that she could not close the framelock if her life depended on it. Was it the thumbnails again?! I dunno. We were able to loosen it up enough that she can now at least operate the knife and she carries it daily. Not sure if she ever uses it.
I'm still considering options for a self defense type fixed blade but I'm starting to wonder if there is any perfect option short of a handgun.
Anyway sorry for all that but my advice would be to go for a slipjoint like a UKPK unless she's very comfortable with locking knives.
