All I ask is that you make clear of the flashback when it happens. A lot of people have trouble with this and it actually takes readers a few lines before they realize they're reading something that happened in the past.
Present tense can work, seeing as it's a flashback I think. It gives good contrast.
example;
"She waited at the bus stop, the streets around her almost deserted. Slowly, her eyelids began to droop and her mind began to wander.
'It's seven o'clock and her dress rips along the hem, causing her to give a cry of anguish. She's late and she knows now there's absolutely no way of getting to her destination. Not now with her dress looking like this. She ties up the lose threads and hobbles back through the doorway.'
Her eyes snapped open as the sound of breaks squeaked on the bus as it rolled up in front of her."