That's stuntwoman Nancy Young in an uncredited bit role.
You've seen Guy Standeven in something because the man was in everything.

Yeah, she's clearly a decoy for anyone actually watching the movie.

I know she was Russian mob, the camera even focuses on her once or twice in a foreshadowing move before the ambush. And further, I think that she might have been tailing Alonzo all day, as she on the outside appeared to be a middle class mom, so he wouldn't even suspect her

This is plausible but still. He's running for his life from an organization that's more like an army than gangsters.
ALTOBELLO YOU beep!!

Yes but remember Jake took his badge. At this point on all appearances he was an armed man in a shot out Monte Carlo busting a red light. The last thing he needed was to have a patrolman waste time checking him out.
I've had a lot of sobering thoughts in my time Del Boy, it's them that started me drinking!

My question is, why would Alonzo even bother to stop at the traffic light? He is a such bad ass that shows no remorse, yet he obeys traffic laws at night with the roads practically empty. I enjoyed this movie but come on!

The Russians probably knew that Alonzo would have his radar up if he spotted a man pulling up beside him, but he might not be on guard if he saw a woman.
May I bone your kipper, Mademoiselle?

And it looked like her vehicle that was behind him blocking him in when he was shot.

She was likely used as a distraction more than anything else as her appearance would not have led him to suspect she was a mafioso, leading him to fall into the spider web trap they were about to set up by not attempting to speed off right away after observing her.

In league?She IS Russian(and in the mob).

"That's a hell of a Caucasian Jackie" -The Dude