Hey Justina how are you... Hope You and Lala are doing absolutely fine.
Well, see feline leukemia can be of different categories. Their risk also varies from one individual to another. Any kind of surgery is of high risk in any given patients of depressed immune system or feline leukemia for that matter. So I would recommend you to find out the risk involved in that.
In an another way if we look forward, you can go for spaying because it will reduce the vertical transmission or in simple words she will not reproduce anymore so spreading of the disease will be stopped.
And I really think that you should go for spaying. Although risk is involved but I think the advantages outweigh the disadvantages.
Thank you
Good luck.