I agree with Doug and Miwokhill, if strings are breaking like that, there’s almost certainly something wrong with the violin set up - a sharp edge on the pegs, nut, bridge, or tailpiece, cutting through the string. I haven’t changed my strings for six months - probably about time I did, but I haven’t noticed any degradation yet, and at $30-40 a set, I prefer to wait.
Where the strings are breaking (and is it one particular string all the time, or the whole set?).
If not breaking at the pressure points mentioned above, are they breaking where the left hand fingers press them down to the fingerboard, or maybe where the bow is crossing the strings near the bridge?
If it’s where the fingers touch, maybe your wife has very acidic sweat and it’s corroding the metal, though to do that in 2 hours she must have sweat like Alien Facehugger blood. Is this 2 hours constant playing, or 2 hours spread over several days?
She should wipe the strings down after playing, to remove sweat and rosin dust.
Is it possible you have the strings tightened up too much? That can promote breakage, though as I know you are an experienced musician this doesn’t seem the likely cause.
Regarding brands of strings, they break down into three types - gut, synthetic core and steel core.
Gut strings may sound wonderful, but they cost a bomb. I don’t know anyone who uses them, probably only professional soloists or people with money to burn.
I personally dislike the sound and feel of metal core strings - to my ears they lack overtones and warmth, but golly they’re loud (too loud). I tried Helicores, and didn’t like them (on my fiddle).
That leaves synthetic core, into which the Thomastic Dominants that Miwokhill mentioned come. Dominants are a good and popular string, and tend to be good on any instrument, but may not necessarily bring out the best in your wife’s fiddle. Other options to Dominant, and slightly cheaper, and Corelli Crystal and Pirastro Tonica. I’m trying both and have been happy with them.
I’d also recommend the Kaplan non-whistling e-string, especially for a beginner.