My wife is 5'1" and 120lbs - she has had no troubles with my XDMs or Glocks. The only thing she doesn't like is the 1911, because the plunger in the front is a bit tough.
It sounds like you just need to learn how to use leverage in your favor.
Hold the gun in your right hand in a shooting style grip. Point the gun to the left and get a firm grasp on the top of the slide. Force your hands together to move the slide to the rear, rather than sling shot style - my wife has trouble with sling shot style, too. With this method, you're using your upper arms and shoulders to compress the spring.
Kind of difficult to explain, I suppose, but look up YouTube videos. I'm sure there are some demonstrations.
Glock 19 G4 BFG | Glock 17 G4 FDE | S&W M&P 22 | Ruger GP100 4" | Sig P226 MK25 | HK USP 9 | HK USP 45 (Tan) | HK P2000 9mm | HK P30L 9mm | HK VP9 | Walther PPQ 9
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