im assuming your not paying to a loan right? I havent looking into it but i know a grip of people would buy $500 Gift of College gift cards and using that towards payments. The loss of value should be around 1% + time to purchase. could be worth looking it up if the school does charge a higher percentage.
depending on your card holdings, id branch out now. I suggest the SPG cards right now as those cards may not exist in the future. Could be a good time to apply and hit the bonuses. Marriott Biz could also be a good potential. hitting these card is a good idea right now.
Downgrade is possible after a year, you do not need to pay an annual fee. to make sure i dont get hit with a fee, i SM chase talking about a downgrade, they will tell you when to reply back again.
She will still keep her UR points but she will lose the ability to transfer to partners. You wont be able to PC out of the UR point system so nothing to worry about. Keep in mind(this is a loophole), she can always go back up to a CSP or CSR when she needs to, but you may get charged the AF.
She can transfer to partners BUT also know when the points expire with the partners... once you send them to partners, the time to expire starts ticking... It would probably be best to keep them as UR since you would have more options to transfer to when u do need them. unless u have something else in mind.
Lastly, Rent with chase and Plastiq. Yes, rent is still working on all 4 cards. The problem might be if you are sending it to a person' name. Easy peasy, show them the lease if they ask to prove your rent. If that does not work, theres always radpad to try out too although its a .5% more than Plastiq.
Suggestion would be to add her to all your long AoA credit cards. It may pass the AoA off to her giving her good credit!
Hope that answers your questions... good luck! :]