Could this be undernuting?

One of my Oaxacan Sativas has this going on with a few of the larger leaves, wonder if its "normal" looking or if theres something I can do? Anything tell-tale about this leaf? I tried to keep colors as true as possible.

Buds look healthy and the smaller leaves look good... She's on day 37 flower, PH is strictly controlled to adjust to 6.5 runoff in 50/50 soil/perlite, this one has only gotten 1/4 of my normal feeding schedule (ie fed only 1/4 as often - plain ph'ed water the other times only fed twice in last 37 days). Temps high 70s, good ventilation, 30%ish RH, distance from light ~ 12 inches or so. Everything else seems to be thriving on the standard nute schedule, including her sister

I'm going to go for Calcium deficiency as a first choice and K def as another possibility.

Yikes, how long do you expect those sats to take to finish? With a fsater strain I'd worry a lot less but if you are [as I suspect] less than halfway through, I'd definitely work on it.

Thanks for the input stinky. Hmm Calcium deficiency.. I have been doing some research and apparently the plants can absorb the calcium, magnesium and manganese in my wellwater, therefore no need for Cal-Mag+ I have been told. Since this is the only plant showing these symptoms, and since I have been feeding it less, a K deficiency is quite possible. I'll give her a little kick of cha-ching tonight for some calcium and micros, and see if that helps. As far as finishing time, who knows? Damn sativas. At 37 days it doesn't even look close, so I'm maybe 1/2way?