Leaf Is Yellow, Brown And Purple-Red!?!

[HopefulAlligator]

I'm HopefulAlligator, AKA Allie. This is my first post here, thank y'all for having me.

I've had orchids before, but it's been years. I've been planning on getting more, and today I made a big leap and decided to buy and try to rescue the few orchids I saw in the 'bargain bin' at my grocery store.

They all seem mostly in decent shape: a few yellowing leaves, a bunch of cracked tips, most things typical of stressed and mistreated orchids. I have well-ventilated, heavily-slotted pots and a bag of good mix on the way, so repotting will be happening as soon as they come in the mail.

The main concern I have is one has a large leaf that is yellowed all the way from its base, but has brown and purple-red coloring near the tip. (See picture for coloring and size specifics.) It is slightly droopy, but still plump. I've been looking around online ever since I got home, but I can't find anything like it. She has one other leaf that is yellow, however it seems to be a natural loss of an old leaf, as it is also drying.
Is this something I need to worry a lot about?
Is cutting it off the best course of action?
What will happen if I cut it vs. if I don't cut it?
Do I need to keep her separated from my other babies? (It's not squishy or slimy, just indentations in some spots.)
I hope I'm not being obnoxious with my worrying. I just really want to give her a good life and address her problems ASAP so she has her best chance. So I'm stressing a bit.
Thank you all so much!
-Allie