"Accidental" exposures can happen anywhere at any time, so no need for any special events. Anytime Luiza goes out, whether with you or on her own, there is the potential for some sexy fun. And no special clothes are needed, though some lend themselves to greater opportunities than others; while a "turtleneck" shirt has limited chances for downblouse, it is perfect for going out braless... maybe with a jacket or front button sweater [jumper] layered over it. Same for semi-sheer tops under another layer. Even a front button shirt can have 1 or 2 extra buttons undone accidentally, or maybe the threads partially cut so a critical button pulls off, or a couple buttonholes are slightly enlarged so the buttons will not hold very well and there is nothing Luiza can do and she would not even "know" that she was maybe showing a little more. Obviously shorter skirts / dresses lend themselves to simple flashes, but so do wrap style skirts / dresses / tops, and front slits in skirts / dresses which can show a bit of thigh with each step and the sides fall back whenever she sits, or not if she does not want them to. My wife has a conservative looking knee length wool skirt she wears to work that has a front center slit that effectively can make the skirt into a ~ 23 cm miniskirt. Add in high heels [high heel boots are best] and stockings [hold up or real] and it looks very demure but can be very hot...
If Luiza works or takes classes these things can happen all day and be innocent accidents so no one she knows would form a negative opinion, though most males and some females are going to really like what they see. Any time going shopping, taking a bus / train / tram to wherever and going out with you are opportunities. Going to other areas than near your home / work will make it easier to go a little further in revealing Luiza's beauty to others.
Most importantly, going slowly and above all making certain you both are having fun and enjoying this are the best ways. Let us know what you do. Good luck!