When does it become the tenant's responsibility to pay for repairs?

[Jim Bouchard]

We have a reasonably new tenant who's had several repair issues since she moved in back on July 1. She had issues with her kitchen faucet leaking. We repaired it at no cost to her. About 2 weeks ago, she contacted us with similar issues. We had a plumber replace the entire faucet, again at no cost to her. 

Las night, she sent a text (along with a video) showing that the hot water doesn't come on from the kitchen faucet. She said "it's weird, doesn't happen all the time." Our plumber will go take a look at it today. If it's related to the work he did, he won't charge us.

In the same text, she showed a picture of her tub hardware, which has come apart from the ceiling support. 

Is this just normal "wear and tear" we should expect? Is there a point where repairs become the tenant's responsibility?

Thanks for your help!