I recently purchased this blade here & it works perfect:

https://www.amazon.com/gp/product/B07M8S99BD/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1

& this website walks you throught the process

https://www.sdivadesigns.com/2020/11/29/using-a-cb09-blade-with-your-silhouette-cameo-4/

What does she want to do with it? I think there's a special blade for foil and stippling. Premium cut and deep cut are $12 a piece and are the basic necessities (IMO) but you could blow her mind if ya showed her a CB09 blade holder.

CJRSLRB CB09 Graphtec Blade Holder Base with 18Pcs Cutting Blades (30/45/60 Degree) for Silhouette Cameo 1 2 3/Portrait/Curio/Graphtec 6000/CE 5000-60 Plotter https://www.amazon.com/dp/B07M8S99BD/ref=cm_sw_r_cp_apan_glt_fabc_QPRF8SAVSXZKCM113CQ1

THE ISSUE BEING idk if the CB09 will work in a cameo 4. So I would compare specs or look a little further if interested in that

Amazon link Here's a link to the one I got! I definitely had to wedge it in there, but the adapter does close all the way for me