Sorry for your loss. Just sharing my experience, may or may not be helpful. Feel free to ignore. I lost my dad about 5 years ago now, different situation to yours as we had a complex relationship, he was an alcoholic and not an easy person in lots of ways (although absolutely brilliant in many others), but in common with your loss it wasn't a quick or easy last few years and we had quite a lot of time to process the inevitable although his actual time/manner of death was still a shock. Like you I felt pretty OK afterwards, got back to my usual routine pretty swiftly, didn't take a lot of time off work or anything (which I know some people did find odd , cold even in me, although they did they didn't say so in as many words), carried out outwardly functioning very normally and didn't feel all that much different internally either. Like you I was a bit worried whether I was 'doing grief right' and friends even tried to persuade me (very kindly) to 'let it all out', 'make time to grieve' , and I did try, but it never really worked for me, I could sit there thinking sad thoughts or looking at pictures of him or listening to his music and I still just didn't really feel any huge wave of emotion or anything. The only time I really felt any very strong emotion or cried lots of tears was at a very, very inconvenient time some months later, at the wedding of a close relative of DH's when it really wasn't appropriate to have a huge emotional meltdown. So I went from trying to make myself feel something to having to make a huge effort to hold it all in, not entirely successfully (sorry SIL and BIL, hopefully you continue to believe those were uncharacteristic happy tears)😔
Anyway the thing I think I learnt is you really can't schedule your feelings or grief in the way I was trying to, it isn't some kind of pressure vat situation that builds incrementally and can be vented in a controlled fashion, feelings aren't logical or predictable, even if like me logic and predictability are the cornerstones of your entire personality so I would like my feelings to play ball please 😂. It didn't really make sense to me that I was effectively numb or perhaps 'shocked' about a death that was not unexpected and in many ways a relief, then full meltdown at an unconnected and otherwise very happy occasion, then go back to mostly normal after, but there we go. That is what happened. I subsequently had some bereavement counseling to try and make sense of it all and without going into all the complexities around my personal story with my dad, the conclusion I came to is that grief and loss just is what is, you just have to roll with it. Sorry for the lack of any real wisdom.
I think the best advice I can offer is just don't worry about what anyone else thinks or does, if you feel up to your usual routines and things that make you feel good, do that, laugh if you want, feel relieved or at peace or even joyous if that's what you feel (I'm sure that's what your mum would want), but if other more negative feelings pop up too, even unexpectedly or at bad times, you can't stop that happening so you just have to live with it... Grief isn't something you go through and then is over, you've always lost that person and you will always feel something about that, the nature and intensity of the feelings may shift over time but they're never gone away...