I would ask the PT for the proper mixing instructions.
I’ve never heard of this combo before, although I can ask my girlfriend about it tomorrow. She's been a physical therapist for over ten years.
Do you live in the United States?
If so I’m surprised your PT suggested using DMSO, as I don’t believe the US FDA has ever approved the solvent for human medicinal use.
On the other hand, I’ve talked with many people who’ve used it and they RAVE about its effects – even when used just by itself.