What is happening to her?

Becareful about reacting to older leaves. always wait to see it it progresses elsewhere when it's some sort of minor issue, mottling etc.. e.g. the one with the tip of the leaf being so close to soil likely touches it occasionally an probably why the tip has symptoms. but, in general older leaves do not remain perfectly pretty all the time and it's not anything to worry about if it is isolate dand doesn't progress elsewhere. burnt tips - a bunch of stuff can cause that from deficiency to toxicity.. not enough information to help you on that. the leaves are not overly lush and they hold themselves up despite being nice and fat. I don't know why this is so obviously "overfed" lol. could be high p, k or s. could be low s, but that would coincide with some petiole-out paling on new growth too. both high p and k would also result in chlorosis in new growth. Reference any leaf symptom chart. these are not opinions. you can see the possibilities then cross-referencen with your behaviour the last several weeks in regard to fertilization and make an informed choice... sometimes being patient and seeing how it progresses is wise too. if you've bumped the concentration up lately, dialing back may be the smart thing to do. don't assume the most recent behaviour is the cause. nute-related issues are about weeks and months of time and rarely a matter of days.