Bra help

[StillNoFuckingEyeDeer]

Hello.
Lookong for some bra advice for my mum. I've tried measuring her the proper way, as advised on here, to get a better fitting bra. She's wearing a 36G (I think), which is a compromise between standard measurements and proper measurements. She feels it's s good fit and more comfortable.
Recently she's been having a lot of problems with her bra straps falling down all the time, no matter how much she shortens them. She does have obviously narrow shoulders, but it hasn't always always been an issue.
Is it just a matter of shortening the strains even more, or should she be looking at something else?
Thank you.

Look at the bras that convert to racer back.

Bravissimo also do one with straps in different place for this.

If it's a compromise, it's probably too big in the back? But she finds a tighter fit uncomfortable?

What brands is she wearing? Some are quite stiff and going straight to your proper size would be a challenge. What about some stretchier brands like Curvy Kate, in her correct size?

She wears M&S bras. A tighter fit is uncomfortable. Racer back is a great suggestion. Thank you.

you can also get clips that allow you to convert any bra to racer back option.
www.amazon.co.uk/s/ref=nb_sb_noss_1?url=search-alias%3Daps&field-keywords=racer+back+bra+clips

She almost certainly needs to go down a band size as that's normally the cause, but changing bra style could help too - look at plunges and full cups instead of balconies and balconettes as they tend to have the straps set slightly further in to the centre of the bra.