I say, start by reading these sites:http://www.paintercreativity.com/articles/top-10-lies.htmlhttp://www.graphicartistsguild.org/resources/contract-monitor/letter-of-agreement/
Now with that in mind, here's my advice: You want to have a project cost estimate, not a hourly rate. And school doesn't necessarily determine your worth.
Yes, as rae333 mentioned, designers charge an hourly rate. But there is also the cost of materials and the copyright/usage rights.
1.) Determined how long the project will take you from start to finish. How long the process from start ideation to the final work for one piece? Ask if there is a date the client wants the work finished by. And what is the final work? You mentioned they were going on tiles, but do you create a print-ready file? Some type of stencil? Actual tiles?
You determine how much you are worth for an hour. Federal minimum wage is $7.25 a hour. Keep in mind almost half of what you charge you hold back for taxes, so you would need to charge $14.50 an hour to make minimum wage. Some designers starting out charge $20 an hour, there was a illustration project I did where I charged $75 an hour.
2.) What material cost are there? As I mentioned above, what are the final works ( print-ready file/some type of stencil/actual tiles) and what is it going to cost. If she wants...stencils, the cost of the acetone and x-acto knives are part of the project estimate.
3.) Copyrights and usage; when you create work, it is yours. You sell certain rights to use the work to someone for a specific time period and use. So if you okay the use of your designs on tiles, they can't be turned around and used on...tee shirts. Not without your say-so or more money for you. That the sketches you made of designs that were rejected aren't used by the client to be made by another (perhaps cheaper) artist.
GAG spells it out - http://www.graphicartistsguild.org/resources/contract-monitor/letter-of-agreement/
Now, make up a contract that clearly spells this all out:
-who it's a contract between
-what work will be done
-when it's due
-how much it'll cost
-all the other good stuff mentioned by GAG
Also, if you go to the library, just get the GAG.. um sorry graphic artist's guild handbook. They have boilerplate contracts in the back of the book for use. Just photocopy them.
Most state colleges, universities and communtiy colleges have graphic design programs. I went to art school. I didn't major in design, but I'm a pretty good designer. Some of my design work - http://gwendolynart.com/portfolio/Gwen-Richards-Resume-Graphic-Designer-Illustrator-09.pdf
But you don't necessarily need to go to school to be a designer. School can teach you how you basic skills; lay out a page/poster/logo/brochure/web site/etc, work with typography, and make things look nice and pretty. Or you can teach yourself with software, books, practice, and tutorials on youtube and the web.
Yes, a college degree is important to people and potential employers, but it doesn't necessarily have to be a design degree. But you're more then technical skills, and that's what you show people to get work. Talent and ability matter too.
Also, there's a LOT
of business stuff to it that you
do running your own design business I've found, instead of designing: finding clients, bills, contracts, promotion, bunches of other stuff. It is MUCH harder to go in on your own then working for a firm. Crap, I typed a lot. Hope this helps.