Some time in the early 1990s, QE2 decided that only she and the Duke of Edinburgh would attend the state opening of Parliament. This was in a bid to show a slimmed down monarchy, more focussed around QE2.
This was then changed again around 2013 (I could be wrong by a few years) when Charles & Camilla started to accompany QE2 and the DoE to Parliament. This was with a view to preparing the public for a potential change of reign.
The peeresses, i.e. wives of sitting Lords, were not impacted by the change above. However, under Blair, the Lords were reformed and all hereditary peers barring 92 were removed. Keir Starmer now proposes to enact legislation removing these 92 as well. If they go, their wives (and their tiaras) will disappear from the chamber.
The Queen's Companions will not be impacted by this. They attend as part of HM's party, and not as peeresses.