I had a big problem because I rarely update my bank passbook since i do most of my business with internet banking. If you don't update your passbook regularly, the bank aggregates your transactions every three months. So when I showed them that they couldn't really tell how long the 800,000 baht had been there. Sooooo, if you too don't get your passbook updated regularly (and transact a lot of business online) be sure you go to the bank and get them to print out ALL your transactions for the year just to be safe.
I don't think the forms are rocket science but you should start the process soon in case they keep sending you back for something you forgot. Also, if you renew it, no matter when you do it, the visa will always have the same start date etc. as the current one.
Yeah, but she needs quite a few documents and since the ones required keep changing all the time, how does she find out which ones she needs? Also, I think it's better to renew it while it's still valid rather than start all over again later. I imagine there are way more hoops to go through with a new visa (health checks and who knows what) than with just renewing the old one.