For thinking this isn't a compliment..

Context is important but it sounds like you took it in the pejorative.

I'd take it to mean nothing big had happened to you recebtly...eg no job changes/illness/house moves etc. Just plodding along basically.

Otherwise your mum would have launched into the story of your new job/bad flu/new house etc.

Just ask (in a light hearted way)

It sounds like a compliment meaning - you’re unproblematic and just get on with things.

why don’t you ask her?

To me this would just mean "no change since last time you asked". No big change in job / relationship etc to report. There might be a certain level of implied criticism if the person saying it would like there to be a change (eg if you've been single for a while and your mum wants you to meet someone and settle down).

What is your relationship with her like?

I would take this to mean that someone is a bit difficult but you love them and can't change them.

Tone of voice is impossible to convey… That would have more impact on the meaning than the words she used.

To be be blunt, it sounds like you might be being a bit over-sensitive, and perhaps that’s how you often appear, hence the comment.

What made you feel hurt by this?

It sounds quite negative to me, but context is everything

I say this response often about DD2. What I mean is she has been her usual happy kind self, sailing through life, doing her own thing, generally unaffected by the world around her. She is consistent in a good way. Context us everything though and the people I say it to know her personality. If she was known for being miserable, dropping out of everything, regularly spending nights in the local Nick and cocking up everything she touched, it would obviously take on a very different meaning...
Only you can say if your DM views your character traits positively and therefore if it was a compliment or not, but whichever it is, she sees you as reliably so.

Personally I think it sounds quite an affectionate thing to say. That they both know you well and that you are quite an individual and they accept you for who you are.
Doesn't sound hurtful to me.

If I said that about someone I suppose I'd mean she was fine, living her life, getting on with it, no drama. But I wouldn't as it suggests dullness.

I'd take the context into consideration. If she said this when something major and good was happening in your life since she last saw the friend - Socks got a big promotion at her job, Socks is nominated for an Academy Award, Socks is expecting a baby - I'd wonder why she didn't say so. If something "bad" happened - Socks lost her job and can't find another one, Socks is getting divorced, Socks has been arrested for murder - I'd think she didn't want her friend to know about it. In this case, I'd maybe ask her why she didn't share the news with the friend.

If nothing much has changed, perhaps "Socks is Socks" is her way of summing it up. Maybe she feels you're always OK no matter what? - which isn't an insult.

Context is everything.

“Crones is just Crones, isn’t she” from my mum would mean I’m up to my eyeballs with activities with the kids, gardening, volunteering, basically keeping many plates in the air and offering to take in more stuff.

The same from my dad would mean I’m meticulously researching things, making lists and possibly spreadsheets.

My MIL would use it to describe an unjustified optimism when I should expecting the worst. (She likes a bit of doom mongering)

My grandmother-in-law would mean I was being a lazy feckless heretic wastrel sponging off her wonderful grandson and ruining his life.

It’s not a negative thing unless she sees you in a negative light.

I'd take that to mean you're your usual self, whatever that may be.

For some reason, to me, it may suggest that you may be a bit quirky. And your mum's friend knows, and that is fine.

I wouldn't think of it as anything negative myself.

I've never heard the term and have no idea what it means. Sorry, I'm no help at all, but what do YOU think its means?

Depends. I might take it as ‘socks is just socks, she’s a one off, authentic and won’t change who she is’ ?

What was context/tone of voice?

She could mean...'Socks is as happy-go-lucky as ever', or 'Socks is busy working hard as usual', or 'Socks is killing it as always', or 'Socks is busy helping everyone out like she always does', or 'Socks is busy being parent if the century to her kids', or a million other positive things.

It might be whatever insecurity you have (we all have them), making you jump to the worst possible conclusion.

Depends how your Mother sees you, but that's pretty irrelevant because what's really important is how you view yourself.