The fact that this plant recently made a flower indicates it is healthy enough and in conditions appropriate enough to do so. Deborah didn't mention any issues with the plant, just the soil.
Vinegar has a very low PH. I wouldn't use it as a treatment of this type for soil or roots, especially on something that likely has no relationship to the plant. If there is organic matter in the pot, it will decompose. There may be too much for optimal conditions but unless the plant is suffering from chlorosis or has some other foliage issue, I wouldn't treat it for anything. It might be happier if repotted if it's been in the same pot/soil for 18 months but I would think that would be because of root congestion, not the unknown product of decomposition being discussed in the soil. After 18 months, any organic matter has likely reached its' final stages of decomposition. The presence of some type of fungus/mushroom is evidence of that. People don't take medications without having something wrong with them, or knowing what's wrong with them, this kind of treatment seems similar to doing that, IMVHO. Like if it ain't broke, don't fix it.