Miltassia in trouble

[Cinderella]

Here are a couple of pictures of my Miltassia which bloomed for me in October 2004! It was fine and healthy at blooming time. Afterwards, I repotted, but used the same medium, so not too much disturbance. It has 2 new growths, but they are not growing much now.

All of a sudden at least 3 leaves looked yellowish and are in fact turning. A couple of days ago I noticed these brown spots on 2 of the leaves! It does not look good.

Should I isolate?

I do not want to use chemicals right now while they are growing inside ..baby, dog and cat are around. HELP!