Welcome to the forum...
She must have accidentally used "someones code" to arm in instant.
Do you know all the codes that are on the system? You will have to go thru them to try to disarm the system (that 4 digit code and 1(off)).
Let us know what you come up with, there may be another way thru programming, but you wont like it.
Are you monitored? Can the dealer provide you with the code after he confirms who you are? Or download and disarm?