Hey, Tina.
I second what XNUMERIK said, and given that I have worked with a number of nonprofit clients not all that far from you, I'll add this...
I previously worked with 1,600 nonprofit clients and fully managed sites for maybe 100 or so. For those clients, we budgeted a certain amount of changes into their monthly contracts so that, while yes they were paying for them, they didn't feel nickeled and dimed every time they wanted something updated, a new page created, etc. In some of those cases, we gave clients minimal site access, but not enough that they could potentially mess things up – delete the home page, take down the whole site, and so on. Hopefully, you at least have the ability to create new pages and content yourself. If not, you might consider moving to a provider that will give you full content access... if that is an option of course.
If you choose to move, you have a lot of different options – Wordpress, Squarespace, Drupal, and more. All have their advantages, and all of them have a plethora of design and site management shops dying to find new clients. Unfortunately, in my experience (and maybe yours as well), recoding for a new platform can be very cost-prohibitive, and then depending on how you have your contract set up with your vendor, getting technical help can also be expensive sometimes... not to mention that choosing the wrong provider is not only a huge headache, but also costly.
All in all, your site looks good, but that being said, there are things that I would change – move context setting to the top, increase font size in most places, merge the blog into the site, change the nav items, put much more emphasis on getting email sign ups, and so on. If you haven't gotten one already, apply for a Google Grant. I used to run one for a client that did somewhat similar work to yours, and for only the cost of my management time, we were getting +$18,000 in monthly GIK AdWords spend from Google, which sent over 26,000 monthly visitors to their site and added to the positive increases they were seeing in donations, email sign ups, social media activity, and more. If you're not doing that already, you probably could be.
I hope that helps. Best of luck.