It's funny - no one is questioning if the .270 WSM is adequate or not for elk. That's not the issue. It's a great round and plenty capable of doing the job at hand (taking an elk.) The question is the recoil in the hands of the OPs wife. I don't know her. She might be immune to recoil and we can all happily recommend a .375 H&H with a muzzle brake and limbsaver pad and say as long as the stock is fit right, it will work great and - besides - our 9 year old shoots that combo 100 times a day at half MOA out to 1000 yards. Ugh. Just silly. Give me a break. (And not a muzzle brake because those things are horrendously loud and obnoxious and a definite a "no" in my book for a HUNTING rifle.)
Thankfully
@jebel posted a great pic that should have helped put the recoil of the .270 WSM into perspective:
The recoil force of the .270 WSM is nearly double the value of the rifle she is currently shooting (.243 Win). It is even 2 ft/lbs more than the .30-06 which many feel is about the upper recoil level the average MAN can tolerate without developing a flinch. This doesn't even show recoil VELOCITY, which is also a player in how a rifle 'feels' to us in terms of recoil, and the .270 WSM has MORE of that, too.
If a .243 Win is just too light for comfort, then perhaps the .25-06 firing a 115grain Nosler Partition would be a good compromise? The recoil is not too brutal and the killing power is quite good. I'd hate to see a happy hunter who is comfortably shooting a .243 Win being put into a hard kicking (and fast kicking) .270WSM and deciding hunting wasn't her thing after all. No point to it. What she is shooting now will legally and legitimately kill elk. A .257 Roberts or .25-06 will do it, too, with only a little more recoil. Going up from there gets into recoil territory that may or may not be tolerable. I think the 6.5 CM would be great, but the OP says "NO" to that option. That's fine. We all have our reasons for things.
If it MUST be a .270, then perhaps the tried and true Winchester version firing a light mono bullet (Barnes 100gr or Hammer 117gr Hunter)? The lighter bullet will kick less, but being a mono, it will still expand and penetrate well. Good luck. Hopefully whatever cartridge/rifle combo that gets chosen it ends up working out for all concerned. (Oh yeah, the CAMILLA rifle from Weatherby really does fit women properly. That would be a great place to look for a gun that FITS her 'out-of-the-box'.)
https://weatherby.com/store/vanguard-camilla/