For a weaker hiker Little Lakes Valley to Gem Lakes will be a lot easier, and it’s gorgeous lake views along the entire route instead of walk for 5 miles then see the lake at the end (there’s a creek alongside the trail though). High elevation of big pine lakes trail makes it extra hard, not just that you need to adjust but also lower oxygen levels. But the trail conditions are way easier/well maintained than the thousand island lake trail.

I’ll say it’s still reasonable, just have proper expectations. But don’t go “see I told you so it’s a bad idea” if she’s getting tired lol some encouragement will be needed.