Yes the M&P is a great choice and is in stock here
https://gun.deals/search/apachesolr_search/022188083903
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The ruger SR22
budsgunshop.com/product_info.php/products_id/712018423 />----------
The Walther P22Q
budsgunshop.com/product_info.php/products_id/111597 />------------
And the Ruger LCPII
budsgunshop.com/product_info.php/products_id/132417 />-----------------
Taurus TX22
nwarmory.com/product/product-tau-1tx22141
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Are good options too.
You can also use handgun hero to compare size and features.
The Walther p22Q has a smaller grip in every over the MP
handgunhero.com/compare/walther-p22-q-vs-smith-wesson-m-p-22-compact

Jack, the M&P15-22 Pistol grip works with a wide range of hand sizes including small hands. Also the same for the Kel-tec : budsgunshop.com/product_info.php/products_id/111461/kel-tec+cnc+cp33blk+cp33+22+lr+semi-automatic+55+33%2b1+black+ -- Cheers and stay safe!

Smith & Wesson M&P15-22 Pistol grip is small and would work fine for your wife. If not, you can change the grip on it since it works with any AR 15 grip. I hope this helps!