My girlfriend can lift heavy objects, so maybe that?

For real though, strength isn’t gendered. There’s strength of character, there’s fortitude, there’s physical strength. But the thing is your final sentence belies a failure to understand just how much these gendered ideas are bullshit. Like whatever the answer is is just whatever the individual values in women that’s difficult. And more scathingly, what is traditionally called feminine strength is the capacity to endure what men do to women.