You didn't ask for this but here I am anyways: please don't return to menu after completing (or failing) the level, it would be nicer to just restart the level/go to the next one straitght.
One small frustrating thing I noticed was the grandma getting caught on something and not moving at all. Perhaps she could walk slowly or slide along an obstacle?
Completed all levels but 5. The third one took the most tries (about 7-10, I don't remember the exact number).
Levels 3 and 5 felt too hard for me. Perhaps it's the combination of not having much control of the grandma, having to slow down, and grandma not being able to walk. Also, probably my skills.
On level 5, not knowing the locations of hydrants and having a strict (IMO) time limit made it too hard for me. Perhaps I could make it with enough tries but whatever. Also, there's a small disparity: in the menu it says that I can hurt grandma no more than 15 times but it's actually 10.
Not that sure about the difficulty, perhaps it's just not my kind of game.