I would really question the amount of wash loads required. Remember these are sheets and towels, the heaviest and largest pieces normally washed. I would not wash more than say 3 sheets and 3 towels. (it does depend on the size of the machine) If you have bigger loads it will wear the used machine faster.

I've never had a wax, but for a massage I hope the are washing two sheets. So let's say each load is 3 sheets and 3 towels, that 1-1/2 customers. If it is true that you will only need to do 9 loads max, that is 15 customers. Math, 15 customers times 2 sheets and 2 towels = 30 sheets and 3 towels. Oh that's 10 loads.

Does she only have 15 customers a week? I don't know the right number! Is it just her or does she have other waxers? If she has other waxers, 15 customers is way to low.

You can massage these numbers however you think needs doing, but don't short yourself.

Maybe a per piece price would be better, in fact what happens if you find you are doing 14 loads a week, and you have the washer and dryer? Do you just give it back?

And it looks like you are talking about $2,500 a year, can she take over if you need to go out of town, or have exams, get sick or whatever, how stuck are you for $2,500?