Honestly so many people today are trying to get into the foot scene. And after staring at hundreds upon hundreds of pretty pairs of feet, what seperates hers from anyone else's? On here? Onlyfans? Feetfinder?
I personally wouldn't pay for foot pics because there are so many free pictures of beautiful girls feet online. Not only that, but I'm more into tickling than feet alone. If, however, she were ticklish and decided to make tickling videos, I would throw money down for that. But it would also depend on whether or not she were willing to show her face and full body.
Not to sound like a parrot or be repetitive here, but there are a lot of women trying to get into this industry. Foot pics are arguably one of the fastest and easiest ways to make money, as well as tickling. With a near endless source of beautiful women willing to show their full bodies, faces, feet, strip naked, etc. and get tickled on top of that, not to mention customs, it's hard for people unwilling to commit to the same terms to break into an arguably growing/oversaturated industry.
I'm sorry if this isn't the answer you and her are looking for, but honesty is the best policy. Will she be able to sell some foot pics? I'm sure she would. But I don't think she's going to get rich alone off of pics similar to what you posted above. I don't even think it'll be decent monthly income tbh.