Well if it is a slide release issue then a Smith & Wesson M&P does not have a lever. It is more like a button. The one on mine is like a hair trigger. My 10 year old niece can work one, as well as several older ladies with arthritic hands can work the one on my well broken in M&P. I know she may not be big on going to gun stores. If so then do not push it. Though I would ask her why she is not big on doing so? When she awnsers do not, and I repeat do not give a quick awnser back to her. You do not in anyway want to look like you are making a sale to her in order to get her to a gun store in any way at the time.
If it is a deal that she is interested becase she is appeasing you then just buy what you want, and like. If she does not like it then you can shoot it. I speak as a married man with a highly opinionated wife. If I try to sell her on something she has said no on, it pushes her farther to her unyielding point of view. Sometimes she warms up to an idea later if she does not feel pushed. It has to be her idea.
Now if she is intersted, then let her know that if you both go to a gun store you do not have to buy anything, and it is acceptaple to ask to see one you are not going to buy. It is also perfectly fine to handle mulitipe guns, and not buy a single thing.
If there is a range with rental guns anywhere near you it may help if she is willing to try a few to let her. If not then do not push it.
The thing is never, ever, ever do you want to push it with your wife. If she say no. Take it for an awnser. You will both be way happer that way.
No matter how many times you do it and nothing happens it only takes something going wrong one time to kill you.