It's warming up, but weather can swing wildly. It'll probably mostly be dry.
I'd have at least a water capacity of 4 liters, and to camel up heavily at water sources. Make sure you friend knows what it means to camel up. If your friend is a slower hiker, more water will need to be carried.
Tell your friend to carry Asabat's PCT Water Report. Very important!
Halfmile's PCT maps will help too. Halfmile tracks and waypoints can go onto a gps too.
It's probably too late to buy Yogi's book, but that'd be a great resource to have. Shipping is Priority, so it'd probably be delivered in 2 days.
The trail is pretty gentle, but the rocks still out there can be painful and tedious when you're walking all day.
Make sure your friend has clothing treated with permethyrin, or buy new clothes with the Insect Shield treatment...although I don't think they sell pants with it, and pants are where I think it's most important.
Sun protection is important, and often forgotten. I had never seen sunburn blisters until I'd seen PCT hikers, and then I saw a few. A full brim hat isn't even enough to protect the face unless your friend has very dark skin. It's best to use some sunscreen on face, neck and hands. I'm assuming long sleeves and pants will be used.
It can be VERY windy. I hope your friend knows what it means to rock stakes.
Don't forget that Warner Springs is closed. No gas station, restaurants or resort this year. Only the post office.
A mail drop can also be done to Paradise Valley Cafe, although doing a drop there means carrying all that weight up Mt. San Jacinto. It might be better to drop into Idyllwild from the Devils Slide trail to resupply.
Is your friend taking the bus back from Cabazon? There's Grayhound there. Public transportation runs to other cities too, but it's kind of difficult to link them together.