Holy shit, that's a bad idea. I mean, Aunt May is a font of aged wisdom for young Peter Parker, as well as a burden that complicates his life, and keeps him grounded. But she's a plot device, not a character in her own right. She has essentially no agenda of her own - she's long since retired and was widowed at the beginning of Spider-Man's career, so she's just kind of there. And she wasn't anything extraordinary in her time - Aunt May and Uncle Ben were simply good normal people who raised their orphan nephew and made sure he had a normal childhood. Which is great for Peter Parker - he's unlikely to think of himself as a 'god among insects' due to that upbringing. But to make a movie about Aunt May? There's nothing really there to make a movie about!
It's as bad an idea as making a TV show involving everyone from the Batman universe except Batman.