Elbos flaring IN during the bench?

[AceDeuce]

I have somewhat of an odd question. I'm training a girl right now and her form is pretty good in the bench (elbows tucked, good arch, shoulder blades tight), however, whenever she is struggling with the last few reps, her elbows move inward. I've never seen this happen before. She says it helps her power through that point. Any reason why this might happen and if its something to be concerned about? If so, how should I go about correcting it. thanks!

[Terry Monk]

She's got to be tucking her elbows to recruit her triceps. I find myself doing it too. Concerned about? I guess not really but it's taking away from the actual point of the bench and doing nothing to improve her weak area.
I would have her start doing wider grip bench with a lower weight to have her concentrate solely on her elbow positioning.