This is a tough case. A solid argument could potentially be made for both sides of the issue.
Allergens, such as molds and seasonal allergies, could potentially induce the immune system to make more antibodies and as such worsen the rheumatic diseases. I am not aware of any data showing this to be true; however, theoretically it is possible.
The flip side of the coin is that there is mold basically everywhere and attempts to reduce it are generally unsuccessul, so would gardening or landscaping worsen the issue? It is difficult to say that it would and just as difficult to say that it would not.
Here in Arizona, we have a fungus known as coccidiotis immitis (valley fever). The fungus lives in the soil and infection cases increase significantly following windy conditions or in places where the dirt is being disturbed (such as in construction areas).
Regarding the inability to take steroids, this is an issue I cannot comment on as I do not know this patients medical history. In general, intolerance of steroids is very rare but does exist.
Best wishes in resolving this issue.
Advice and opinions given are based on the information provided and must not be considered an official medical recommendation. The limitations of the internet prevent an appropriate evaluation. Always consult your doctor if there is concern.