Firstly, I'm not a great fan of street candids unless there's a connection between the subject and the environment or some other reason that makes the photograph interesting. To me, this is lacking anything special that would warrant pressing the shutter in the first place. If it were a photo of Dame Judy Dench waiting outside a theatre, then the point of interest comes from the subject, but as this image is of a stranger, the photographer has to create the interest.
Leaving the above aside, there are a few ways in which I think the image could be improved.
The lady is far too central in the frame. She's looking out of the frame towards the right, which means that the eye naturally moves from left to right to follow her gaze, but it also means that the lefthand third of the frame is wasted space. Cropping to about half to two-thirds the way into the stonework would improve the composition dramatically.
Cropping as above would also solve a number of other issues. It looks to my eye that the image has either been shot or straightened to make the edge of stonework on the far left vertical. This is the least important vertical line in the composition and as a result, to my eye, the edge nearest the subject seems to be falling in at the top. In a shot like this you have three options, 1) straighten to make the shot look natural which usually means getting the most important lines as vertical and horizontal as possible and letting the others go, 2) correct the distortion in post processing, or 3) crop out the worst of the offending lines. Either 1 or 3 would work in this instance, but s the image would benefit from cropping anyway, I'd correct the verticals at the same time.
I feel that the hat is getting lost in the shadows and needs to be brought out to define the subject.
I'm not keen on the B&W conversion, but I think that if you play with it a little you could get a more pleasing look, but tonally it's quite flat so I'm not sure how much leeway you have there.
If I were to shoot this subject I'd have taken a completely different tack and approached her. The light's nice so there's potential for a flattering portrait that tells a story. Normally, because I find there's little interest in the legs and bodies of ordinary folk, I prefer headshots unless I can tie the subject in with their surrounds or there's a compelling reason to go longer. For this subject, her NHS style walking stick tells a tale, but so does the pearl hat-pin which adds a very subtle air of elegance to her otherwise ordinary appearance, so I'd look for a composition that would include both elements.
Hope that helps the OP. In the end it's all opinion and there's no real right or wrong in art, but there are generally held views which are the closest thing we have to rules in photography. I'll sign off with the old gambit that you need to know and understand these rules before you can break them
Maybe you could add a touch of contrast to bring her out of the rather drab, overall picture.
