Joined projects in the form of breeder loan where everything is written down yes but joint ownership, I would not recommend it.
If the animal belong to each of you 50/50 who will have physical custody?
Who will pay for the care (food, housing etc)?
Who would pay for vet care? Would it be 50/50? But what if the animal requires vet care due to the actions of the person who has physical custody? Who would pay for the bill? What if the animal dies?
Less face it a female Mojave is not that costly save up some money and buy one that will be yours and then do breeder loan with your friend if that is what you wish to do (it will be less of a headache in my opinion)