I think it is insecurity... people don't want the RESPONSIBILITY of thier actions... most of us don't feel secure enough to adsmit that we have faults... so we redirect the blame on someone or something else.
It isn't her fault- it is 'tired's' fault (no doubt she is tired because of work, kids, illness or something else- so it is their fault)
It isn't her fault she forgot your birthday- it is yours (why didn't you tell her you wanted a gift? haha)...
It isnt her fault she ran into your fence- it is the dog...
it isn't a sincere apology, but it doesn't reflect on you, it probably reflects on her insecurity more. She is so afraid her mistakes will reflect on her character that she cannot just say "I am sorry, I was wrong" or "I am sorry I forgot you" or "I was not paying attention, I am sorry I ran into your fence".
A few years ago I resolved to try to NOT make excuses for my actions... I do what I do, and if I screw up, I am responsible for it. When I REALLY screw up, it is HARD not to shift the blame away from myself... but by taking the responsibility for my own actions I do think it has made me a more careful, compassionate and considerate person. I cannot say the "devil made me do it" anymore... so I try harder not to screw up in the first place. BUT it is something I did, for myself. if her apologies offend you, I guess you could say something to her... but since you aren't her parent- she might just think you are being stuck up or something...
-M.