OP, the only thing I would suggest in any conversations you have about this is that you tread lightly when pointing out that you're a volunteer. Organizations can and should still request and require improvements and standards in work even if the people doing the work are doing so for free. If you feel the requirements are excessive or the people enforcing them are unreasonable, you may express it or you may quit, but whether or not you're doing the work as a volunteer or a paid employee is irrelevant.
I do think your idea of asking for an improvement meeting for after the holidays is a great solution.
As a volunteer, OP may be providing services that organization may otherwise have to pay for. For example, OP may have extensive experience in that particular database program. Would TPTB of an organization want to lose an experienced volunteer because she was being harassed and bullied? Would they want that to become public knowledge?
I must confess I don't know the acronym TPTB 
I haven't seen any evidence of harassment or bullying. Annoying pestering? Yes.
Again I do think it's reasonable and appropriate for the OP to request a formal process or scheduled review rather than having to field the board member's "ad hoc" and potentially ineffective suggestions as they come. I just think the fact that the OP is a volunteer has nothing to do with the situation. Yes it's a kindness to the organization but it's still appropriate for the organization to have a say in how it is done. Whether or not the OP is paid for it is moot.
I think it is relevant. There is a different dynamic between a volunteer and employee vs. a member of the board. The woman can natter at POF all she wants while POF is on the clock as an employee. She's wasting a volunteers *personal* time when she pesters POF.
I too am glad you aren't apologizing.
I agree with Eden in this. There is a difference between "making suggestions" and "bullying" and I don't think it's necessarily out of line for someone to make suggestions on work that is done by a volunteer. Where it does make a difference is in the expectations for a volunteer to follow through. And TPTB may choose that it's more important to have the work done for free than it is to require that certain changes, that may be good but too time consuming for a volunteer to do, be made.
I don't blame the OP for feeling harrassed and overwhelmed by all these suggestions. But it's all in the delivery...on both ends. For example:
Suggestor: I have a suggestion for the database. Why don't you do X
OP: Thank you for the suggestion but I have experience doing that and it actually doesn't work that well.
or
OP: Thank you for the suggestion and while it's a good one, I don't have the time or the resources to implement that. I am a volunteer and cannot dedicate any more time than I already do.
But if the Suggestor is being a bully and harrassing the OP, then that is the conversation she needs to have with the President. The problem wouldn't necessarily be that someone is making suggestions, but the manner in how they are doing it. And if the problem is the frequency of the suggestions, then the answer may be some sort of policy on how and when suggestions are offered.
I work with both volunteers and paid employees and I don't differentiate between the two when I make suggestions on improment for work that they do. And I treat each with the same respect. The only difference is that I can require a paid employee to do what I suggest, regardless of their opinion, that I can't do with a volunteer. But I don't temper suggestions for improvement based on hiring status.