Assalamu'alaikum w.w.

It is immodest and impermissible for a Muslim woman to
uncover herself in the manner described, during
wedding receptions for a number of reasons:-

(1) Wedding receptions are seldom pure from
intermingling no matter how much effort is made to
enforce segregation. If not free and open mixing, a
few males will find it difficult to resist the
temptation to satisfy their nafs and will wander in
and out under various pretences.

(2) The intention to uncover their Hijaabs/Abaayas,
etc is as you describe to show off their fashion,
hairstyles, jewellery etc.

Hazrat Abdllah Ibn Umar (R.A) narrates that Rasulullah
(sallallahu alaihi wa sallam) said, "Whoever wears an
attire of show in this world, Allah (SWT) will make
him wear clothing of disgrace on the Day of
Judgement."

(Musnad Imam Ahmad/Ibn Majah)

Allah (SWT) Knows Best.
(Mufti) Abdullah Patel.