Lots of female Heads of State habitually wear/wore trouser suits or trousered outfits, so I doubt it was really a big deal for our Head of State to, you know, cope when she met them or their partners.
It was literally the late Queen's job to meet and greet, and show hospitality to other Heads of State, their partners, and representatives. The thought of the UK's long-serving, experienced, tough and eclectic HoS indulging in negative emotions over a trouser suit seems extremely unlikely and has the whiff of misinformation about it.