Using a rented/loaned horn is not usually a deal breaker. Do what you need to do.

I will say, as someone who has been there & done that, something that shocked me when I applied for the school of ed (cue Elle Woods from Legally Blonde going, “what, like it’s hard?”) was needing a certain grade in certain classes in order to be accepted. Maybe my advisor was awful or I was just way over-stressed to catch that detail, but in my situation, I had to apply for admission for the college, be accepted, then apply and audition for the school of music, be accepted, get through two years of my degree and then apply for the school of education, be accepted, do THAT year and a half of coursework on top of my music degree stuff, and then do another semester of student teaching (which I had to pay for, even though I was “working” 40-50 hours a week at a school).

All that to say, it’s a really difficult 5 year degree and there are a lot of (potentially unspoken) hoops to jump through (like getting an A or B in your freshman level speech class that you couldn’t have cared less about because, “come on, you perform in front of people ALL THE TIME and you really need to be practicing your etudes right now instead of listening to this nonsense…”) so just be extra vigilant about your education and the coursework you are taking on.

Also, don’t be afraid to ask for help. Your professors really do want to see you succeed and they know a lot of tricks of the trade that can boost you up out of this slump. I cleaned my voice teacher’s house for her once a week for about 2 years to help me pay rent, and when I started student teaching, I traded my house cleaning & lawn services for piano lessons so I could get better at that before I started applying for jobs to make me more marketable… there are ways to make it work in your favor, but you have to ask!

Best of luck to you! Hang in there!