It's not peak moving season, but if you're targeting young professionals, you would have more luck than students right now. Are there many 24-28 year old working professionals in your city?
I "renew" roommate posts on craigslist daily.
All the "have parents co-sign, ask for 4 semesters of transcripts, talk to employer, credit check" are things I don't do. I run their PACER and court record search, I do rental history, I do criminal history, and I do basic job/school/income verification.
I wouldn't have her list specific ages like that. 24-28 is the ideal target, not something to advertise. Just put "full-time working professional and studious student seeks same in a roommate who has a day job/school outside the home" or something, noting that it's a very quiet home, not a party house, few visitors, etc. If someone comes along who's 29 or 30-35 and are a good match, she should consider it. It's the 18-21/2 crowd that are usually too new to rentals to appreciate it, and are too whiny as roommates, and more likely to still be party types.
She'll want/need to go co-ed to get decent applicants... usually females above 25 are hard to find. Too many live with their boyfriends/husbands already, if not their female friends. I also always listed "absolutely no smokers, not outside smokers, not inside smokers" on my roommate listings, blaming asthma. Otherwise, you get outside smokers, and they bring that horrid smell inside even if they actually go outside to smoke every time (they often don't, especially in snow/rain... and crack a window, at best). I don't allow vaping or pot either.
If she allows short-term rentals (with 30 days notice) and month to month, she'll have better luck filling rooms right now. (And potentially more vacancy later. Personally, I always keep a roommate listing ad up on craigslist all the time, empty room or not. I don't add photos to the listing. That gives me a constant array of people to email when a room opens, as I do short-term roommates often.)
How much is she charging for a deposit? 200-300 is probably the upper cap. If someone could afford $500 in rent and a $500 deposit, they'd probably get their own apartment.
Is she allowing pets? Pets can damage, but I say "crated pets ok." No outdoor (not good weather, and noise would bother neighbors) and no pets wandering the house without their owner present. I don't allow cats. Allowing pets, especially larger pets, adds some new potential tenants. I had a roommate with a 100 pound lab that even had the dog wear dog shoes so the wood floor wouldn't be scratched, and he took his dog to dog day care and training regularly. I had a 10 pound dog with a careless owner who jumped/scratched on my doors/windows and peed on the floor all the time. I had to get rid of that roommate. And add "crated dogs" as one of my rules. The owner is the problem with pets, not so much the dog size.