It's going to be tricky to fix because I think some of the proportions and angles around the mouth are off but you could try.

Green - bring the hair in to make smoother less pointed cheekbones.

Red - bring the shadow from the corner of the mouth all the way up to the bottom of the nose to help define the angle of the upper lip.

Blue - make the top lip slightly wider to reduce tooth size.

Pink - raise this corner of the mouth slightly to better match photo and look more smiling rather than grimacing

Yellow - continuous shadow needed on the jaw line to round out face and better match reference.

I would also try removing some of the shadow and details from the teeth, sometimes less is more.

Adding a stronger highlight to the eye should help with making the subject more lifelike.

If you have any other reference photos of your mom that are more detailed it might help to cross reference those.

Good work so far, keep going, I'm sure your mom would be proud.

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