Who must pay for the emergency all out?

Other

Last night at 00:30 my tenant had a problem getting into her front door. There had never been a problem with that door but last night apparently the lock could be moved with the key but the door still did not open. Even though the house has three lockable entrances she was unable to get in because (until last night) she had only been carrying the key for the front door on her key ring and had effectively blocked the main back door by purposely leaving a key stuck on the inside to make the house "burglar safe", as recommended by a friend. She tried to contact me at 1 am but I did not get the message as my phone was on charge in a different room. So she called an emergency locksmith who could not open the front door and then had to destroy and replace the back door lock as this was the only way to get past the blockage created by the internal key. The locksmith was at the premises until about 3 am and the bill is an eyewatering £235. While I'm obviously responsible to repair the front door (if that is what is needed, I have already contacted someone to check this out) I don't feel responsible for her blocking her alternative options to gain access and ending up needing an emergency call out in the middle of the night who then has to take drastic action to get past an obstacle that my tenant has created. My opinion is that if she had carried the key for the back door as well instead of blocking it on purpose all this would have been totally avoidable and I could have taken the necessary action during regular working hours in a considered way, obviously at my expense. My own opinion aside, who will be legally responsible for this bill?