Okay...my thoughts...
Is the third candidate used to working with younger clients? That would be important (since her current charges are obviously school age). And what would her school schedule entail during the year. When would she be working on her homework? I mean, a 35-hour a week job with school on the side can lead to burn out. If she is part-time school, it would be better. I just know I did one semester of full-time school with Julia and felt wrecked after the 12th week. I believe I used some excessive sick time those last few weeks...although would have to ask Julia's mom if she remembers to be sure. I learned to only take part-time classes (but I was with Julia more like 50 hours a week).
The first candidate...how were the references?
I think they speak the most for the candidate at hand. I would need hers to be glowing. But after 9 years, I would imagine they would be. Why is she moving to Portland? Any family close? Also, the most concerning thing with her is that she might have her own "parenting" techniques after nine years. Which could be great if they match yours...but could be a downfall if they are different. The benefit of a younger candidate is the "learnability" of them.
The second one..I wouldn't discount her just because of the hours. In lots of ways, caring for only one family at a time is easier than multiple small jobs. And more rewarding. The references remarks, and her youth, both would lean me that direction. Plus, I see her potential happiness with salary as a bonus (I imagine the first candidate is going to be rather pricey). But I see your concern with the hours being a big change. Has she every held a full time job of any kind? Is she local? Is her family local? Do you know if she lives with her parents?
I am giving you no answers...and more questions
But my gut reaction in relation to each candidate is (in order of top running to third running is):
Candidate two
Canidate one
Canidate three