2 suggestions for you:

1) I used to carry my maltese in a backpack carrier. That worked well, but I wouldn't have wanted to do it for long.

2) Buy a used kid's trailer. Cars tend to give trailers a wider berth when they think there could be a child inside. Your doggie would probably be safer because of that than anywhere else. Plus, there's less distance to fall should something happen. Harness not collar to attach.

I doubt there's much that would seriously protect from a direct car hit at high speed -not a criticism (I used to bike with my doggie until he passed on), just an observation. I would focus more on typical bike accidents - falling over, wheel getting caught, etc. and making sure she's protected in that kind of situation.

CA