My mum treats all of us, and our own DC, the same. Makes an effort to see us all, spends time with the grandchildren, spends the same on everyone at Christmas/birthdays, helps us all out when we need it, babysits an equal amount, etc.
In terms of spending time together she spends the most time with me as I live nearest to her, I'm just a few streets away, I'm also a SAHM so im available in a way that my siblings aren't. Because if this a lot of the support work falls to me, it's not that my brother's arent bothered it's just that proximity and availability mean I do it. So things like popping round to put her bins out when she's on holiday or looking after her dog, waiting in for parcels or workers if she's at work and it clashes, looking in on her if she's not well, calling in for a cuppa and a chat, etc (to be fair, she reciprocates). I know for a fact that when she gets old if she ever needs care it will be on me, my brothers can be very single minded, they're usually nowhere to be seen when there's donkey work to be done. For example when mum moved house it was DH and I who were helping with the packing and lifting, DH who put all her curtain rails up, fit her burglar alarm, etc. I can see why in other families where the situation is similar that this results in the mother favouring the daughter(s).