Does Mary's (peace be upon her) saying: "Oh, would that I had died before this and been a thing forgotten, completely forgotten" indicate her displeasure with Allah's decree, knowing that the Prophet (peace be upon him) said: "Many men reached perfection, but none among women reached perfection except... and Mary, daughter of Imran"?

Maryam, peace be upon her, wished for death out of fear of people being tempted by her and suffering religious harm, not out of discontent with divine decree. It is permissible to wish for death when there is religious temptation (fitna), as the sorcerers did when Pharaoh tried to turn them away from their religion, and as Ali ibn Abi Talib and Al-Bukhari wished for death when trials (fitan) befell them. However, wishing for death due to personal harm such as illness or poverty is discouraged. The Sunnah (definition) is to say: "O Allah, keep me alive as long as life is better for me, and cause me to die if death is better for me."