Google ad sense and ranking your site on Google listings through thorough search engine optimization aka SEO is pretty much the basis.
Every year or so Google changes up their algorithm, that's the best time to rank, if you can figure out what the new algorithm is looking for.
Depending on what platform she's using, there are probably already good tools for setting it up and checking your seo. Every page should have a long form keyword, that is repeated often. Example "cast iron cooking over fire" as well as several short ones, like "cast iron" or even just "cast". The more specific you are in your keyword choice, the better your chances of naturally ranking are.
Amazon affiliate links are another good one, but easy to overdo, and if you don't make enough turnover sales they'll suspend your account.
Traffic traffic traffic. SEO and getting eyes on the page can and will take more time than actually writing the blog.
There are others, some pay better, some don't pay, but good luck digging through pages of ranked blogs talking about them to find the actual useful information.
If it's just a personal blog, something like live journal used to be, there's no point. The past several years have seen big big pushes to become wikis instead of just blogs. Places that contain all or a vast majority of information on what the blog is about.
Go recipe hunting. All the paragraphs and paragraphs of useless E36 M3 above the recipe? That's there to help rank on Google and drive traffic and ad revenue. Same as with every other niche.
Understand you're a niche writer. Learn everything, share everything, and hope you are not in an over saturated niche to begin with.
Figure out the best ways to reach out on social media. But Facebook ads and use their information to narrow down the people that will get them as likely to click on it and check it out.
You really need to whore yourself out on social media to get traffic, not just new traffic, but repeated traffic, that will engage and share your content