Mary might have chosen to re-visit Jesus's tomb “with spices” (to mix with water) in order “to anoint” Jesus's body. Two evidences:
• …Mark explicitly reports that this was her reason.1
• …Mary would want to anoint the body2
Mary would anticipate that the stench of Jesus's rotting corpse would be overwhelming by Easter morning.1
• …The body would not have been in the tomb very long.2
• …Mary knew that aromatic spices had been put on Jesus's body3
Mary would at no point fail to notice that she could not move the massive blocking-stone at Jesus's tomb.[See evidence and response]1 This would obviously be relevant because, in conjunction with other reasons, Mary's knowing Jesus's tomb was sealed would be sufficient to deter her from visiting it.
◦ Christopher Bryan (NT professor at Sewanee): “…if there were any reminiscence behind Mark's story [16:2-4], we would surely need to admit that Mary of Magdala and her companions will hardly have been the first or last people in the history of the world to have been moved by strong emotion to attempt something without knowing how they were going to do it, or even without noticing until the last minute an obvious difficulty.” [The Resurrection of the Messiah (Oxford, 2011), 76.]So if the prior probability is higher that Mary would notice before setting off, it need not be that much higher (i.e. the argument here is not particularly strong, contra Brown, The Death of the Messiah, 1311.).
Mary would know that soldiers were guarding Jesus's tomb.1 [See response]1
But, so what? Couldn't it simply be that…
• …the women's emotional state clouded their judgment.3
• …the guards would not care to prevent the women's entrance.4
• Matti Kankaanniemi: “Friday and Sunday, while - in all likelihood – they spent the Sabbath, the Saturday, ‘the day of the guards’, at someone’s home. In the Markan storyline when the women arrive at the tomb the angel is already seated on the rolled stone. It is therefore possible, in principle, that the women never saw a single guard at the tomb, even if guards had been posted there.” [The Guards of the Tomb (Åbo Akademi, 2007), 29.]