[nzporsche944s2]

You don't mention the cost of the upgrades or whether the current lease is a better deal for you or her.

One way would be that you could fund it at your cost in return for an extension of the lease and an agreed increase at intervals during the term of the lease such as annual reviews based on the official inflation rate or CPI (if you don't already have such a clause). That way you have the security of the longer lease and a price movement mechanism.