Aviza, how is your relationship with your mother in general? Are you girls friendly and close? In which case you could try to meet her for coffee, treat her to her favourite snack and then explain to her nicely that it is impossible for you to take care of her dog for so long. I have often found people to be more reasonable just after they have eaten something comforting. If possible you can offer to visit her house x times a week, feed the dog and take him/her out for a short walk. For the rest she can arrange another minder. Will that be helpful? If nothing works, take a leaf out of Divine's page and go mia. Stop taking her calls, don't reply to her texts and when the day comes, go visit your favourite restaurant.