This brand , 'Blue Streak Toilet chem' is good down to 10F. It would become slushy rather than a solid freeze at 10F. Call the mfg of her brand and ask.
I found my interior temps of my TT to be about 5-10F warmer than the outside air . I never had any brand freeze at outside temps in the single digits.
If still concerned about it or need peace of mind :
What about mailing a trailer key to someone in Indiana ?
If no key is available to give to someone, call the mfg and have them send a new key using her vin # for the trailer. If she doesn't have the vin#, there are ways to get it. Her dealers sales invoice or her insurance company will have it.
Remember, she only needs a dedicated key in she dead-bolted her TT lock. If she only used the paddle lock, its a universal trailer key .