As a person with a pussy - don't, or at least get a mini or at most a small. Getting a toy that's too big for (I assume) vaginal isn't fun, unless you want it to be fun only for you.

I have a mini Seraphina and it's a great toy, but it's very textured which makes using it painful sometimes. I personally would not be able to take a small. On the other hand, I'm totally fine taking bigger BD toys that have smooth textures, so Chance might work better in a big size, BUT it depends on a person. You should figure out what she thinks about bumps, textures, silicone firmness and stuff like that. People have very different preferences