You have to put your foot down. No permission to buy an enlarger is a no-go. Get some polysulfide toner and tell her that the smell would not occur if you just had an enlarger! Of course, there is a danger that she will get her stuff an leave you, in which case, you don't need to ask anybody for permission anymore, and you get a lot more room for the enlarger.
Davids idea is a very good one, but the neutral-density capability of Ilford filters is unfortunately highly sophisticated and useless. Not that any other filter does a better job. They all try to satisfy an impractical ISO standard. But go with David's idea anyway. That will work.
Let me know if you need the recipe for polysulfide toner.