I have always been wary of "Co" officers, because it's usually born out of two people who want to work together, not because the job is set up that way. So, what often ends of happening is that one person does all the work, or everything takes longer because one "co" doesn't want to step on the toes of the other "co", or things fall thru the cracks because one thought the other was doing it.
Now, if you DEFINE the job so two people have distinct job responsibilities, this will work great. And in the final analysis, I suggest you don't have "Co-Treasurers", you have a "Treasurer" and an "Assistant Treasurer".
I currently am our District Treasurer. I oversee 4 elementary schools and a junior high. Each school has two treasurers. The main Treasurer is in charge of the books only. That consists of keeping files, receipts, budget reporting, reconciling bank statements and writing out (not signing) checks. The other person signs checks only. (My signature is also required on large checks.) This is the checks and balances of the system. We have signature and bookeeping requirements and I oversee that they are all doing their jobs correctly by doing periodic audits.
Our district did not think it was a good idea to put a person into the main bookkeeping part of the Treasurer position unless they had previously helped the PTO as a committee head or Building Chair, or in some other larger capacity. We felt the Treasurer position really requires somewhat of a good feel about how things work, and having experience in other jobs would give you this insight.
My first suggestion to you, without really knowing your setup, is to keep cotreasurers, but the new person should only be the check signer. She cannot write checks, but can back the other Treasurer up with helping with records, getting receipts - the whole paper trail issue, if she needs it. Good training to take over next year or so.
Second, read all the articles from PTO Today in the Treasurers report, past and present,and make sure they follow these guidelines. They are GREAT! (not an employee, just a big fan)
Also noticed you mentioned the last treasurer signed all checks herself. We always have two signatures on all checks. One from a parent and one from either the principal. Not sure how other PTOs handle this.
We are currently going through a problem where money has been misplaced/stolen. You have a valid point that the new person should not handle any monies until you get to know her, etc. What we did learn through all of this is that basic accounting procedures indicate that one person should handle the money/checkbook and that another person should receive all the bank statements and balance them to be sure there are no inconsistencies. Maybe the co-treasurer that you don't know very well can make sure all the paperwork, etc. is in order and all accounts balance. It will be a practical check and balance procedure. Just tell her it will be a way for her to become familiar with how things are run.
I'm by no way an expert, but our recent situation has given us some much needed insight. This person that took money from us was very friendly, always helpful, but very aggressive and wanted their hands in the money all the time. We are now wary of these types of people.
We had our first meeting tonight for our PTC. We had elections for every position. One of the ladies who has been helping get things started had wanted to be treasuer. We had discussed today how to run our meeting and had decided that we didn't want co officers. One of the teachers nominated this lady for treasuer. We were about to vote and someone else raised her hand and also wanted to be treasuer. I didn't know what to do so I asked the principal what do we do. Meaning do the ladies explain why they wanted to be treasuer and so forth. Instead the principal said she had been at a school where the ptc had co treasuers. Well a vote was put forth and now we have co treasuers. The lady who wanted to be treasuer has a valid point. That the second lady is new to our school and that we really don't know her. The first lady doesn't want to share responsibilites for liability reasons. Our last ptc treasuer signed all checks by herself and we don't know what the books look like or how the finances are. I have to agree that co treasuers can lead to a problem. How do we fix this? We have other positions that still need to be filled,just not any officer positions. HELP