most efficient one for them (running-economy wise)

I went out on a short shakeout run with someone who was visiting the area the day before he was going to run a marathon and his stride was so noticeably goofy looking I remember it to this day - but he's also the only person I've run with who runs around 2:22 for the marathon (and he hasn't missed any time for injury in the few years I've been following him on my strava feed). My experience with that guy validated a lot of the research out there that basically says "runners find their optimal stride on their own." (And that you can't tell just by looking at a runner's stride if they are going to be fast or not)

... So the short version of it is - it might be weird looking but I'd not touch it if I were coaching her unless she was complaining about pain etc.