May I say a few words in defense of the Master Gardeners program?
The Master Gardeners program was started in the state I live in by Washington State University. Their extension offices in the counties were overwhelmed by questions from the public and they needed help. They decided to start a volunteer program that would provide assistance to homeowners, to free up their extension offices to support commericial growers. The volunteers are educated by the unverisity and the extension offices so this is a science-based program. You don't learn everything, or even an in depth knowledge about particular things. Instead, you are given the tools you'll need to figure out how to address gardening questions and educate the public about
sustainable gardening practices. You learn the basics about plant taxonomy, botany, soils, nutrition, plant pathology and entomology. You learn about weeds, vegetables, fruits, ornamentals and forests. And you learn about how to manage garden challenges like pests, fire risk, drought, heat and
water. It's very broad. The intent is to give each volunteer the tools they'll need to be able to provide research-based information to homeowners about sustainable gardening practices.
So, the question is, is the program right for you? What does your sister-in-law see in you that she thinks you'd enjoy it? Are you passionate about sustainable gardening, like knowing what plants grow best under the conditions in a particular environment or addressing issues caused by pests using means that don't harm the environment if at all possible? Would you like to spread the word? Do you love figuring out a particularily puzzling question? Would you like to meet a whole bunch of people with similar interests? If so, it might be. If you're interested, go talk to the Extension Office coordinator and visit their plant and insect clinic and ask them about their program. Each county's program is different, but I bet you'll find a bunch of nice people who would welcome you into their group and provide you with a variety of volunteer opportunities to choose from.