If you already have the 27, I'd say barrel only...but from scratch..I'd say 26...
Ability to shoot multiple calibers is great, but I found that I never did..so I sold my 23, both barrels, all the ammo and just got 19...chasing down 3 different types of ammo got annoying to me..
Since she has a 26 already, you wont have to get mags (.at least I wouldnt) I think your situation. 40-9 is the good call.
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