The IRS at https://www.irs.gov/publications/p502 defines medical expenses this way in part.
“Medical expenses are the costs of diagnosis, cure, mitigation, treatment, or prevention of disease, and for the purpose of affecting any part or function of the body. These expenses include payments for legal medical services rendered by physicians, surgeons, dentists, and other medical practitioners. They include the costs of equipment, supplies, and diagnostic devices needed for these purposes.”
To make sure you’re getting correct advice, I’d suggest you contact the administrator of your HSA plan, the IRS, or your tax advisor about whether you can count an uninterruptable power supply (battery back-up) for the PD machine.
As mmegee616 says, being able to do manual exchanges is always an option for patients on the PD cycler. Hopefully your daughter’s home training nurse has taught her how to do manual exchanges. If not, I’d ask for that training.